SEOJIN: I think teamwork is what tean leader leads the job and teammates sharing opinions. Teammates have to work together.

CORRECT: I think teamwork is what a team leader needs to lead and teammates share opinions. Teammates have to work together.

SEOJIN: I like working as a group because I can listen to other teammate's thoughts. The advantage of working as a group is that my friend can fill up my disadvantages and we can work together.

CORRECT:

SEOJIN: The disanvantages of working as a group is that you can be uncongenial with your teammates.

CORRECT: The disadvantage of working as a group is that you can be uncongenial with your teammates.

SEOJIN: You can have a fight if it gets worse. Lastly, I think having a team leader is important because team leader can listen to his (or her) teammates and can make decisions.

CORRECT!

>>Be mindful of the correct spelling of words. A singular subject takes singular verb.