Ashlie:
Considering the mobility issue of the wheelchair which requires more space and transportation ease to the parks, I would encourage you to look at the Contemporary Hotel.
The rooms at the Contemporary are some of the largest on the Disney campus and include a day bed for a fifth occupant. Most of the handicapped rooms, however, have King beds so make sure and request a double. But if you do not need to transfer --or the wheelchair is thinner than a standard 'Quickie'--you might not need the handicapped bath and a standard room (especially the end rooms in the Garden Wings) may give you enough space. What makes the Contemporary most desirable is the proximity of its rooms in the tower to the convenient transportation of the monorail that will whisk you away to Magic Kingdom and Epcot. The bus stop is not a long walk from the main hotel and all buses come with ramps or lifts. If you are wanting accommodations for the grandparents also, a two-bedroom villa at Bay Lake Towers next door would be the best choice for the entire group.
If you have your own car, another option is the cabins at Fort Wilderness, although they only accommodate six. The wheelchair-accessible cabins are several feet wider and the bathrooms have lower sides for ease of transfer, not to mention enough room to do a 360 degree turn.
Before you make a final decision, I'd recommend you visiting
www.allears.net and looking at its Accommodations section. There, you will find pictures of many of the rooms--including those that are wheelchair accessible.
Wishing y'all a magical vacation!
Whitney