Yes it is wrong hello English must correct this mistake

Start with small sentences and also use English words in sentence of your mother tongue

In tenses, the verb differs according to the tense. And also to make the verb of the tense, helping verbs + suffix are used, but not in all tenses. In simple tenses, only helping verb (for future tense) or suffix (s, es for present and ed for past) is used, to be, as helping verb, is used in continuous tense and passive construction

Hello

There are five friends in the party

Yes

The answer of a question asked with what is an object and the verb to go is intransitive so your question is not correct

Both are correct

Theirs is a possessive pronoun and it is used without noun behind it. Theirs is a green bag. Their bag is green.

Before the definite noun like the name of unique things of nature, name of rivers, mountains, oceans etc.