If we are late, they will be angry. * Being late is a real possibility, so you should use the first conditional.

There are twenty-two students. We commonly used there is/are to express existence.

IBGE, the Brazilian Institute of Geography and Statistics, is an important institution. Don't take for granted that your readers know things.

My sister is being annoying today, but usually she is nice. (We use progressive tenses for actions that are temporary)

I have not eaten anything today.

You don't need commas if "and" is used to indicate addition.

The teachers* We use "the" when talking about a specific group.

Everyone has seen that movie.

Use a comma before and when adding three items or more.

He is not really nice-looking, and yet he has enormous charm. Use a comma before any coordinating conjunction connecting two independent clauses.

I fell asleep while I was watching TV. *After while use past progressive.

It was raining when I got home last night. * Use past progressive for a longer action that was interrupted by a shorter action in the past.