Getting the reins on a renegade booster group is tough, and can be ugly. If you have the principal and superintendent behind you (in most crazy booster cases, they are tired of dealing with these nutjobs in their offices too) it can be done. I have had a principal tell me that under no circumstances would a certain parent be allowed to be the band president (woman caused him endless grief before I got there). The quickest way is to shut down the organization and start over. If you don't have their backing, you will just have to let time and graduation be your weapon. Work on the newer parents. Get them in your corner and ease them into leadership positions. Pick your battles (i.e. chaperones can't sit in the lobby of the hotel drinking on the spring trip). Put your foot down on the nuttier stuff (with the principal's backing), like wanting to contribute money to the school board campaign against a board member they didn't like and asking several band kids to show up in uniform for a publicity shot. Have to admit I didn't like the board member either, but still had to shut them down. They want to spend too much on the banquet? Probably not a hill to die on.
It is not easy. It can be ugly. Depending on how deep their tentacles go in the board and community (the smaller the district, the worse it can be) it can cost you your job. Good luck.