Can't help you with your location but if you could look for something with a group camping area or loop it might be helpful. We had a family reunion at a campground a few years back and had an entire loop to ourselves. Good thing because we probably would have bothered other campers with all of the laughter that was going on.

I know it is not ideal, but almost all KOA's have Kamping Kabins.  with enough notice and reservations, you could easily arrange it so everyone could go.