My friends are not doing their homework at the seaside. My friends are playing volleyball.
Пояснение: Present Continuous с отрицанием используется для описания действия, которое не происходит сейчас (are not doing their homework at the seaside). Present Continuous используется для описания действия, происходящего сейчас (are playing volleyball).
Ответ: My friends are not doing their homework at the seaside. My friends are playing volleyball.