I would suggest a 4 bedroom pool house in Windsor Hills, Emerald Island or Windsor Palms. A 4 bedroom townhouse with private pool in Encantada or Paradise Palms.
If it was me, I'd look for a 4 bedroom pool house in Emerald Island, or if price is no problem, one in Windsor Hills.
You would have plenty of room for everyone and your own heated pool just outside the patio doors. Even if it is a little chilly you only have a couple of steps and you're in the house.
We've been in Feb/Mar for the last number of years and the weather is usually ok but this year it was chilly everyday that we were there but I still went in the pool at our rental house. Mind you I didn't linger outside once I got out of the pool.
You can find listings on vrbo for all of the communities:
http://www.vrbo.com/vacation-rentals/usa/florida/central-disney-orlando/kissimmee
Windsor Hills also has their own site: windsorhillsrent.com
Emerald Island: stayatemeraldisland.com
These are within 5 - 7 minutes of the Animal Kingdom parking lot.
Map:
http://maps.google.com/maps/ms?ie=U...8.272032,-81.608849&spn=0.068335,0.11055&z=13
Windsor Hills is #1 , Emerald Island #15, Windsor Palms #13 Encantada #17
Paradise Palms #107