The Grand Villas will sleep 12, and they have them at OKW, BWV and SSR. Tinkerbee is right that they are expensive and they do book up quickly, so look into it soon. Rack rates (which is likely all you will get for a GV) range between $1070-1350 a night depending on season for OKW and SSR, while at BWV the rates are more like $1360-$1745 a night depending on season (but with a guaranteed BW view). DVC members try to book GVs very early on, usually 7-11 months out, so the sooner you move on these the better.
Another option might be to get two 2BR units at any of the DVC/ Home away from Home resorts, which is sometimes cheaper. The Grand Villas are magnificent tho, and you will have real beds for 10 ppl and a double pull-out couch for the 11th; most 2BR units have 4 ppl in real beds and the other 4 on pull-outs.
It might be more cost-efficient to buy into DVC. Just a hypothetical here: A 210 point SSR contract will run you less than $20,000 up front (one time cost, which you can finance if needed) plus about $800 in annual maintenence fees. But then if you bank one year's points and borrow another's, you can get 6 nights in a GV at SSR once every three years during summer or spring break (fewer points if at OKW, but those reserve up quickly). The rack rate cash cost of the GV for the same 6 night stay in summer or spring break would be $9,031.50 after tax, so you'd be breaking even in 7-8 years (9-10 if you finance). Plus DVC members get discounted rates on stuff like Annual Passes and at certain restaurants. We are DVC members and love it, since we try to go to WDW every year (4 times this yr!).
Just a thought.
Good luck!