The studios at BWV and BCV only hold 4 people plus a child under 3. There is one queen bed and a double sleeper sofa. A portable Pac 'N Play crib is provided for the child. The villas do not provide rollaways/extra bedding to accomodate parties larger than the stated maximum.
If your family needs a daybed for the 5th person, you will be better off in either the BWI, BC or YC hotels.
That said, the mini-kitchens of the villas are a tremendous advantage over the regular hotel rooms. They include a microwave, sink, toaster, coffeemaker, small refrigerator and mugs, paper plates, bowls & plasticware for 4.
To use the SAB pool, you must be a guest of either the YC, BC or BCV. To use the Luna Park pool at BWI/BWV, you must be a guest of one of those hotels. During the SAB slide rehab, guests of the YC, BC & BCV may use the Luna Park pool. Believe the slide rehab will complete sometime in late March or early April.
If you are renting points to stay at a DVC resort and your resort ID says "DVC Member", you may be allowed to "pool hop" (subject to certain conditions). The pools at AKL and SAB are not available to DVC pool hoppers.
HTH.