The most cost effective and comfortable option would be to stay off site, maybe renting a house. That will give the most space for the money.
If you want to keep your options to the on site resorts, you have a few things you can consider.
You can stay in 1 room at most of the deluxe resorts (all except for AKL and WL I think). But that would be really cramped with 6 people!
You could consider 2 rooms in a moderate, which would cost roughly the same as 1 room at a deluxe. A lot more space that way, but there is no guarantee of connecting rooms.
You could get 2 rooms at Value for much less, but again, no guarantee of connecting rooms.
There is always a family suite at ASMu, or AoA if you're going after May 2012. That costs a tad more than 2 value rooms.
The other option is a 2 bedroom villa. This is the most expensive option when booking directly through Disney, but if you rented points, you could end up paying 40-70% less than the Disney rack rate, which I think may put you back in to the price range of getting 2 rooms at a moderate.