we have 3 kids also and just returned from POR AB. It's the only section that will book for 5. It was myself, my mother, and 3 kids. My ds as the only boy won the trundle bed, one of my dd's slept on a blow up mattress that fit between the beds, the other slept with either me or grandma. The rm was definately big enough, the grounds were beautiful, and the kids loved the pools.
Try for bldg 14, it's the closest to the main bldg. If you're using a stroller ask for 1st fl so you don't have to haul it up the steps every night. Bldg 14 is closest to the south bus depot, which is the 1st stop at POR. We never had a problem getting on a bus, but we did have to stand 2x. You can take the boat over to FQ so your kids can use the pool there, it's geared to small kids. The boat also goes to downtown disney.