tenses - Do these sentences use the present simple and present continuous correctly?

When we do homework, we focus on vocabulary

When we do homework, we will focus on vocabulary

When we are doing homework, we focus on vocabulary

when we are doing homework, we will focus on vocabulary

Are these grammatically correct, please? From what I understand, the sentences represent the following:

1, - habitual action, everytime we do homework, we focus on vocabulary

2, - Not sure if this one is grammatically correct

3 - Not sure either

4, - The present tense represents a future action, for example, in doing homework later on today, we will focus on vocabulary.