Actually, based on what the OP said they are going ahead with #4. Apparently they have a good working relationship with the county, at least that's what he said.

I've commented several times on why I'm less than enthusiastic about that option. They second group of flyers is not a club, has no organization or leader, no telling who and their brother's cousin's neighbor's aunt may show up on any given day to fly. Let's say Joe the Plumber shows up to fly on Thursday afternoon for te first time. Who is going to tell him that he can't fly using channel X? What if no one else is there? Is someone going to post some signs? There is no mechanism I see that is available to enforce or insure compliance. Don't lose sight of the fact that if this group was interested in frequency control/frequency sharing they wouldn't have just shown up and started flying, knowing that the other club existed.

That said, given that the OP indicates the club is going to the county about the situation, I hope the aim is to allow both groups to continue to fly. Responsibly.

There has been all this talk about the club should do this, or the club should do that, and how they are the villians in this.....somehow. Remember that the situation is a result of an ad hoc group of flyers acting in a very irresponsible manner. Essentially they have put the club in a position of having to sort out the mess. I've heard very little criticism of that group, just a bunch of arrows being slung at the club. If this group was responsible, the situation wouldn't exist to begin with. That lack of responsibility is an indicator to me of the likely success of a frequency agreement that no one can enforce.