Well, it seems to me that it SHOULD be simple.
It never is when you have people involved, though...
My thoughts would be:
1) First come, first served. The existing club gets priority over a start up group. BTW, is this group a chartered MAAC club or not?
2) Allocate frequencies to each group and that is that. Kind of harsh and people will have to go buy new crystals, get radios re-tuned, etc. But at least everybody gets to fly.
3) Arbitration with MAAC sitting down with the two groups and hashing out a plan. But it must be FINAL, not a wishy washy thing.
Anything besides these will result in whining, fighting, complaining and on and on. And it needs to be an edict, not a request. If you depend on people to police themselves or sort it out on their own, it will degenerate into a kids on the playground level.
My $0.02 on this... Very black and white, I know. But my experience with people says that you can't do anything else if you expect to have it work. Leaving a gray area or options will lead to somebody abusing it and hurting everybody.
Mark