I think that the OKW 1-bedroom is a good idea except that I'm not sure if you can have 6 in it, even with one under 3. Someone in another thread was saying that with the one-bedrooms that sleep 5, the limit is just 5, not 5 + 1 under 3. I would check into that before planning on it.
Personally, I can't imagine 15 days in two studios with four kids. We use the kitchen and laundry too much, even with our one-and-only child. Have you looked at the point costs for a 2-bedroom at OKW? Or a value 2-bedroom at AKV? That would be so nice for you guys.