Wow, I can say that your situation does sound pretty difficult, and depending on a few things, you've already gotten a number of really good suggestions.
When I was a Junior on my team, I had a somewhat similar issue. Our team wasn't very large and I was the chief engineer, but the teacher sponsor for our school had it out for me. The teacher bullied me and tried to make things difficult, it didn't help that I had him for an actual class during school as well. I also had my dad on the team as a mentor, but he was good about not showing favoritism (we also had been volunteering at regionals before I was even on a team). By the end of FIRST season we had found out that the teacher got the pink slip and wouldn't be working at our school the next year. This was because we had brought up his actions to our principal, who liked the robotics team even if he didn't understand much about it.
So, like others have said, I suggest going to your principal with your evidence, if your team isn't school based, try to contact a local FIRST rep.
If you happen to be a Georgia team, you can PM me and I can help to put you in contact with our regional director or other people. Also if you're in Georgia and end up taking the route of splitting off to form a new team(last resort), I know some people who would love to mentor and help you out.
