I have 6 kids, and usually travel with at last a couple siblings, and assorted gf and bfs. 10-12 has been by typical party size for the last 10 years. and 5-10 people in the 10 years before that.
It is an issue. It used to be that we would book multiple rooms, but sometimes the rooms would not be together. Sometimes, not even in the same building. and this solution really stinks when you have lots of small children, and your MB/Card only works on your specific room. This is a really big issue, and we decided 10 years ago, never book multiple rooms again. If they can't guarantee to put our rooms even in the same building, with small children, then it will not work.
So since then, we have mostly alternated between Bonnet Creek and the OKW GV. Both have large rooms that can easily hold huge groups, with large kitchens, many bathrooms, etc. The OKW GV is about have the price of other GVs. If you spread the cost out between other adults, then its not that expensive (part of the reason why I invite my siblings, haha).
Bonnet Creek is simply gorgeous. The presidential suite is the nicest place I've ever stayed at. And its probobly half the price of the OKW GV. Dirt cheap. I would stay there again but there buses are terrible, so you really have to rent a car, and that really means 2-3 cars so not to burden everyone. And those costs just add up. Plus you loose "benefits". We would end up booking a single day at the campground, or all star to get the benefits BUT WOULD STILL USE THE ROOM. At least, some of the kids would use the rooms, just for privacy or whatever.
That said, my kids are older now. I don't think we will stay at OKW again. In Dec/Jan, we took some small trips down to stay at various resorts for long weekends (ie BC, BW, Poly, AKL), and realized how much we were missing out. So, with the kids older, I'm guessing the next big trip will be 3 DVC studios. The older kids and siblings can be "on there own" so to speak.
Thats the resort side of big groups. Park planning and ADRs are a whole different issue, especially with the statement Disney just made yesterday about sorta banning big groups