Another option would be 2 cabins at Fort Wilderness (sleep 6 each).
A Grand Villa at Old Key West or BoardWalk will sleep 12, but they are expensive and are seldom available for rent.
However, you might want to check out the DVC site on this board about renting the points (you don't have to be a DVC member yourself) to stay there. Especially if your trip does not include a Friday or Saturday night, this can be a very attractive option. Note you'd need to book the full 12 months (or is it 11?) out to try and get a grand villa.
Also, a combination of a studio and a 2 bedroom at the DVC resorts would sleep a total of 12 and cost less than a single Grand Villa (although they might not be nerar each other in the resort, but I'm sure they'll try to get you close).