Мы посидим в фойе, пока актеры буду

Мы посидим в фойе, пока актеры будут репетировать последнюю сцену.

Results (English) 1:

We sit in the lobby, while the actors will rehearse the last scene.

Results (English) 2:

We sit in the lobby until the actors are rehearsing the last scene.

Results (English) 3:

We посидим in the foyer, as long as the actors will be rehearsed prior the last scene.