I know in my district we had a coach who was terrible. It was another sport and bullying wasn't an issue but other things were. Parents talked to the AD for YEARS to dislodge her to no avail. There were two issues behind this:
1. she was a teacher in the district and blah blah blah. They can stay in a coaching job as long as they want it, no one wanted to ruffle feathers, she feels she has a handle on things now, etc.
2. it turned out the coach had a connection to the AD. Aha! It was one of those twisted "AD's mother was godmother to coach's aunt" kind of things, but that's how she got the job and that's how she kept the job. She didn't leave until it was her decision.
Huntington, it seems you've got a real mess on your hands, and it's going to have to become messier if you want to effect a change. You parents are going to have to escalate if you want results. ADs are there for the students but they are also there for their coaches, as it seems is certainly the case in your town. It is very hard to get rid of a coach if that coach does not want to go. Good luck.