Αυθεντικό κείμενο - Αγγλικά - Please let us know when the other musicians have...

This is an e-mail to the leader of a Turkish choir accompanied by a some Turkish musicians from me (a musician who will join them later).

I have tried to translate it into Turkish, but I'm very unsure of one vocabulary word (key) and the grammatical structure, so I wanted to see how a Turkish native speaker (hopefully with some knowledge of music) would translate it.