How do we correctly negate the verb “to be” in the indicative mood, present tense, third person?

Which form correctly expresses the plural negation in the following sentence: “A gyerekek ... az iskolában.”?

Which expression can be used correctly in a short dialogue to express negation about ourselves?

Which answer is correct as a negative response to the question “Te is fáradt vagy?”?

Which form correspond to the negation of the verb “to be” in the plural?

How do we address someone directly if we want to say that they do not belong to a group?

Which sentence is grammatically correct in terms of the use of the verb “to be”?