Проверти, и со вторым надо так же сделать ! 1) we were in the camp last summer. we weren't in the camp last summer? weren't we in the camp summer? 2) my mother was at the concert yesterday

Если второе предложение - отрицание, то следует убрать вопрос )))
Третье в принципе правильно. Но зачем отрицать в вопросе, если в исходном предложении утверждение? Я бы написала так:
Were we in the camp last summer?

My mother was at the concert yesterday.
My mother wasn't at the concert yesterday.
Was my mother at the concert yesterday?