Gv stays are lots of fun if you have a good cohesive unit of people staying there. We have done it with 3 family groups and it worked very well. Each family group had their own bedroom and bath, and the leftovers from the Master room group had the pull out in the living room and their own bath in the hall. We have also done the GV with fewer people, so I was a bit skeptical about the group of 12, but it worked better than I imagined it would.
Good planning is the key! We did a LOT of preplanning with all the groups and had a cooking schedule. Each family group was responsible for the in-villa meals for one day. It was their choice what they cooked that day, and the choice of the rest in the villa if they were eating in with the group or going out. We did all our grocery shopping between the airport and WDW. All the planning helped it be a success, because everyone had input into what groceries etc. Every family purchased their own snacks and the food needed for their day of meal preps.