Could you check and correct my english essay? I wrote them, but I can't check them well by myself. It is difficult for me.

２Are parents best teachers?
Parents are most influential, most kindly, and most dedicated with their children, so many people thinks parents are best teachers for their children. However, parents completely best teachers for their children? Some people thinks that parents are best teachers for their children, but the others don’t think so. In my opinion, parents are best teachers for their children, but they aren’t always best teacher for their children. There are several reasons.
To begin with, when their children are child, their parents have to see and protect them carefully. Children always see around and imitate a lot of things. For example, their parents’ talk. They can take a chance to learn their mother language through their imitation.
In this case, parents are first teachers for their children at learning their native language. Children can learn a lot of things. As example for my neighbor, she always imitated her family’s talk. She didn’t speak well when she spoke first time, but she improved her conversation skill. Her parents are good teacher for her conversation in native language. She can learn a lot of vocabulary , accurate pronunciation, and so on.
In addition, parents can suggest their children for a lot of things. Mostly, their parents can have a lot of time with their children. If so, parents can understand their children’s personality. They are not only best teacher for their children but also their best supporter. In adolescence, most children maybe have a trouble for a communication with their parents, teachers, friends, and so on. Generally speaking, high school students may have a bad communication with their parents. For example, my brother had a bad communication with his parents. In adolescence, people feel like to decide their future. So, they may oppose to their parents’ opinion and decide their behavior by theirselves. However, their parents have a lot of knowledge and information. Parents can give a effective advice for their children in many situations. Children should practice their parents’ advice. If so, children may have a greatest achievement in their daily life.
Last not but least, there are a lot of teachers in many social groups, for instance, school, university, college, and so on. University and college have a significant teachers in many domains. These teachers have their major ,but parents don’t have specific major. If people have their specific major, their opinion may biased in many situation. On the other hand, parents don’t have specific major, so they can have panoramic view in daily life. It is the key to learn and interest a lot of things.
In conclusion, according to the things on the above, parents are best teachers for their children.

I'm going to copy and paste everything and look at it in parts.

"Are parents best teachers?"

This is a bit vague. Change to "Are parents the best teacher's for their children?" or "Who is most suited to teach children?" or "Are parents the most suitable teachers for their children?"

"Parents are most influential, most kindly, and most dedicated with their children, so many people thinks parents are best teachers for their children."

First, I'd split this into two separate sentences to make it easier.
Be careful with "most." There are three different forms: "most," "the most," and "mostly." and they are used in different ways. You are actually pairing it with 2 different kinds of words, two adjectives and a verb. In both these cases, you should use "the most" since it indicates the extreme in an adjective and verbs.
I also think "kind" sounds more natural than "kindly"
You can say: "Parents are the most influential, the most kind, and the the most dedicated with their children."
We are left with:
"Many people thinks parents are best teachers for there children."
The "people" and "thinks" don't match, so the "thinks" must be changed
It sounds better with the "the" article before "best teachers."
You need to use the correct (there/their/they're). "Their" indicates possessive.
"Many people think parents are the best teachers for their children."

"However, parents completely best teachers for their children?"

This is missing a verb."Are" should be added.
Also, "completely " doesn't make sense here. "Always" could work. You may want to be more specific because this is still relatively vague.
Should be: "However, are parents always the best teachers for their children?
Another option may be: "However, are parents able to completely fill the role of a teacher for their children?"

"Some people thinks that parents are best teachers for their children, but the others don’t think so."
Same issue as earlier with "people thinks"
I'd add "the" in front of "best teachers," but remove the "the" in front of "others," in this particular sentence.
This should be: "Some people THINK that parents are THE best teachers for their children, but others don't think so."

"In my opinion, parents are best teachers for their children, but they aren’t always best teacher for their children."
This sentence seems contradictory. Could change to "In my opinion, parents play an important role in their children's lives, but there are some instances when other teachers are necessary."

"There are several reasons."
This is good

"To begin with, when their children are child, their parents have to see and protect them carefully."
Remove "with". "To begin" is a good way to begin a sentence, but the "with" is not necessary.
"oversee" or "watch over" would work better here.
"child" is does not portray any useful meaning here. Change to "young."
Remove one of the "their"s so that there is only one subject in the sentence.
This should be: "To begin, when their children are young, parents have to watch over and protect them carefully."

"Children always see around and imitate a lot of things."
"See" isn't the best verb in this case. never put "see" right next to "around." A better phrase could be "watch their surroundings" or "look around"
This should be: "Children always look around and imitate a lot of things."

"For example, their parents’ talk. "
Since you separated this into another sentence, this sentence needs a verb. You can keep this a part of the previous sentence to avoid repetition.
"Talk" can be used as a noun, but it sounds strange in this case.
You can either make this sentence: "For example, they imitate their parents' speech." or you can combine them, saying "Children always look around and imitate a lot of things, such as their parents' speech."

"They can take a chance to learn their mother language through their imitation."
The phrase "take a chance" is only used when referring to stuff like chasing your dreams or something. Thus, "take" should be removed.
Should be: "This is a good chance for children to learn their mother tongue."
This almost sounds pretty good, but 'chance" is still slightly strange here.
I'd completely remove the "chance," and change the order, making it "Imitating their parents is a good way for children to learn their mother tongue."
Another option could be "By imitating their parents, children are given a good opportunity to learn their mother tongue."

"In this case, parents are first teachers for their children at learning their native language."
I think this sentence just rephrases the previous one, and could be removed. Also, "In this case" sounds slightly awkward here since it is typically the case that people learn in this way. It isn't unusual or specific to one person or group. You could say "Typically, parents are the first people to teach children their native language."

"Children can learn a lot of things."
This sentence is fine.

" As example for my neighbor, she always imitated her family’s talk."
Should be: "For example, my neighbor always imitated her family's speech."

" She didn’t speak well when she spoke first time, but she improved her conversation skill."
Should be "She didn't speak well when she spoke for the first time, but she improved her speaking ability."

"Her parents are good teacher for her conversation in native language."
Should be: "Her parents are suitable at teaching her basic conversations in native language."

"She can learn a lot of vocabulary, accurate pronunciation, and so on. "
This is fine.

"In addition, parents can suggest their children for a lot of things."
This is a bit confusing.

"Mostly, their parents can have a lot of time with their children."
"Furthermore" could be better as a transition word. The "their" and the "can" is unnecessary.
We typically say "spend time with."
Should be: "Furthermore, parents spend a lot of time with their children."
If so, parents can understand their children’s personality. "

"They are not only best teacher for their children but also their best supporter."
Add "the"
Should be: They are not only the best teacher for their children but also their best supporter."

"In adolescence, most children maybe have a trouble for a communication with their parents, teachers, friends, and so on."
"Maybe" sounds odd here. I'd put "some" instead of "most" to indicate that same level of uncertainty.
Don't put "a" in front of "trouble." "Having trouble" is a very common phrase.
"For a communication" is not correct.
Should be: "In adolescence, some children have trouble communicating with their parents, teachers, friends, and so on."

"Generally speaking, high school students may have a bad communication with their parents."
Using another verb or noun may make this sound more natural. While we DO say "we had a conversation," we do NOT say " we had a communication"
This is a bit different from what you said, but this may work. "Generally speaking, high school students may have negative experiences with their parents."

"For example, my brother had a bad communication with his parents."
Could be: "For example, my brother had a bad disagreement with our parents."

"In adolescence, people feel like to decide their future."
Could be " In adolescence, people must make many decisions that may impact their future." or "In adolescence, people feel like they must decide on their whole future."
These two sentences have different meanings. I am not sure which would be better.

"So, they may oppose to their parents’ opinion and decide their behavior by theirselves."
"Theirselves" should be "themselves."
"Behavior" sounds strange here.
Could change to: "So, they may oppose their parent's opinion and decide their own path." or "So, they may oppose their parent's opinion and make their own choices."

"However, their parents have a lot of knowledge and information."
This is fine, but I'd remove "their." It is unnecessary.

" Parents can give a effective advice for their children in many situations. "
The "a" should be removed.

"Children should practice their parents’ advice."
This is fine. While this conveys a different meaning, you could also say "Children should consider their parents' advice, carefully."

"If so, children may have a greatest achievement in their daily life."
"have a greatest" doesn't sound natural.
This could be: "If so, a child may find themselves making the greatest achievement in their life." or "If they do, children may achieve great things in their daily life."

"Last not but least, there are a lot of teachers in many social groups, for instance, school, university, college, and so on."
"social groups" doesn't really make sense. "educational facilities" may work.

" University and college have a significant teachers in many domains."
"significant" doesn't seem right here. "Different" may work.
Could be: "Universities and colleges have many different teachers."

" These teachers have their major, but parents don’t have specific major."

" If people have their specific major, their opinion may biased in many situation."
Could be: "In many situations, having a specific major could make someone more biased in their opinion."

"On the other hand, parents don’t have specific major, so they can have panoramic view in daily life."
"panoramic" is a bit odd here"
Could make this: "..so they have a broader view of life."

"It is the key to learn and interest a lot of things."
Change to: "This is key in learning and being interested in a lot of things."

"In conclusion, according to the things on the above, parents are best teachers for their children."
It would be better as: "Considering all of this, parents are the best teachers for their children."

I hope this was helpful. Your English is great! Let me know if any of my corrections are confusing. I gave some sentences that sound natural to me, but there are many different ways of saying things.