Certain WDW
DVC resorts have studios that sleep five -- Boardwalk Villas, Beach Club Villas, Villas at Wilderness Lodge (now named Boulder Ridge Villas), Polynesian Villas, and Villas at Grand Floridian -- because they have a queen bed, a pull-out couch and a murphy type pull down bed from a cabinet that is under the TV (that murphy bed is somewhat smaller than a twin and is best for small adults, teens or children). Can you do five in those? Obviously yes? Is it a comfortable five? That is a matter of opinion but many of us would never do it because we believe it is far too cramped.
The 1BRs are huge in comparison to the studios. They have a living room with a pull out couch and a master bedroom with a king. Animal Kingdom Kidani, Bay Laker Tower, and Old Key West have an extra pull-out twin chair in the living room, and Grand Floridian has one of those murphy bed arrangements, and thus those can sleep five. The others can sleep only 4, but allow five if you provide your own sleeping materias for the fifth (e.g., a blow-up, a sleeping bag, and any needed sheets, blankets and pillows for same). The 1BRs also gives you a full-kitchen and a washer/dryer. The 1BRs at Kidani and Bay lake Tower also give you a second bathroom.
Personally with five, I would choose a 1BR. If it includes children who will spend a lot of time at Magic Kingdom, I would likely choose Bay Lake, which provides easy access to MK and gives you a very large room and a second bathroom. Grand Floridian would also be fine but significantly more expensive and only one bathroom. Second choice for five would be the 1BR at Kidani, also very large, and a good pool with a very impressive kids water play area. If you want to do a studio or five in a 1BR that has beds for only 4, then BCV would be fine with its access to Stormalong Bay, but Boardwalk would be fine too for the Epcot area. There are kids activities at all the resorts but Animal Kingdom Lodge, both Jambo and Kidani, would be an ideal choice for those with young kids.
As to pools, members have certain privileges to pool hop among resorts, renters from members do not. You do get access to any pools at the particular resort you are staying, e.g., Bay Lake Tower guests can use the pool at Bay Lake and at the Contemporary because they are both part of the same resort.
Be aware that owners of a particular resort can begin reserving their own resort at 11 months out from arrival. Owners of any resort can reserve another DVC resort beginning 7 months out. If you do not reserve by 7 months out, your choices can become very limited. Moreover, though Sep is generally a fairly easy time to get rooms, there are certain rooms that often require using the 11 month reservation window to assure getting them: Animal Kingdom value and club level rooms, Bay Lake standard view, Boardwalk standard and boardwalk view studios and 2BRs, and Grand Floridian studios; BCV studios also have a risk of disappearing before 7 months out. If you want to try for any of those, then what you need to do is look immediately for a rental (and some of those may already be filled for some days you want)