One thing I know is this: If a couple of the employees came to me and said they understood what was going on and they wanted to help me, I would definitely listen. It would be a refreshing change from dealing with the employees that are taking advantage of me.
If I were the conductor and you and your friend presented me with a specific plan, such as a list of consequences for missing practices, I would probably implement it. Honestly, though, I would feel more comfortable if I could announce it like, "I got some helpful feedback about how I'm running the orchestra, and we're going to change things." And then I'd pass out a sheet with the new rules. Because someone else came up with them, I'd be much more likely to stick with it and not let people get away with so much anymore.
(Yeah, I know I'm a terrible manager. Don't worry, I'm looking for a new job.)