My wife and I ran a field station in Bolivia for a couple of years, and had previously worked as volunteers for multiple ecology projects in the tropics. I’ve also worked as a volunteer (with many others) in several theatre productions.
Never did I or others assume that because we were volunteers that somehow meant we had less responsibility… or that we didn’t have to do what was expected of us, and likewise, we said goodbye to volunteers who couldn’t live up to what was required of them (and we required a hell of a lot)....
A goal requiring a conhesive team, requires a cohesive team, paid or not. and once you accept the arrangement, as long as it is honestly spelled out before hand…(ie I will volunteer my time, work with the team not against it, work the hours required, and in return I will get valuable experience that Im seeking), then the volunteers/actors have a responsibility to live up to their agreed commitment.
At the same time, if people have jobs then their prime responsibility is to their employer, not you. But they knew this when they agreed to the rehersals.
So may I suggest that if the timing of rehersals is turning out to be too close in proximity to their work time, that you sit down and have a meeting and come to some compromise with respect to rehersal hours.
I also think you have to remind them very soon and very clearly of their responsibilities, and get rid of anyone who is giving an indication that they aren’t reliable or willing to do what’s required. It’ll send a message to the others…
It might also be worthwhile emphasizing that you’re volunteering too…which presumably you are?
Basically, get everyone together and reclarify what’s required of them. Get it all out on the table, or the play could bomb.
Break a leg!