I think the cheapest would be to get 2 (or 3 depending on how willing the kids are to share beds, which I know can be an issue with boys) rooms at the all-stars. Connecting rooms (in sets of two, but not three, aa far as I know) are available. Each room would have two double beds. This option would likely cost 77-115/night per room (depending on the time of year they are traveling, assuming no discounts, and standard room location).
A slightly more comfortable option would be to stay at Port Orleans Riverside, a Moderate resort, in the Alligator Bayou section, in connecting rooms. With this option, you would get a nicer resort, a little bit bigger rooms, and the rooms have two double beds and a trundle bed. So depending on sleeping arrangements, the 5 boys could have one room and mom & dad the other, or the boys could each have their own bed annd mom & dad could share. These rooms could cost (at full price) 133-194 per night, per room, standard view.
As far as buying park tickets, with that size crew, joining the Disney Club I think would be well worth it. With the Disney club, you can get a discount on park tickets, and potentially a 15-20% discount on the rooms.
Also, it may be worth buying one annual pass for someone in the group, if there is an annual pass discount available; currently these discounts are around 30% off the room cost.
Personally, I would really try to swing the moderate if at all possible. With the right discount, it could end up costing around 200/night for the two rooms, and in my opinion, would be worth it.
I also know there are larger room options available, including 2-bedroom Villas at Boardwalk, Wilderness, Old Key West, and soon, the Beach Club (Which will all sleep up to 8), or a cabin at Ft Wilderness (I'm not sure how many these sleep). All of these options are (I believe) more costly for the room, but have kitchen facilities so they could save quite a bit on meals if they are inclined to cook their own.
I also know there are many offsite villas that may be less expensive, but personally, I think the Disney resorts are worth the money.
Happy planning!