I believe that only some of the fully wheelchair accessible rooms (the ones with roll in showers) have a single king bed. There is more room for a wheelchair with the king bed, but I think they have some rooms with either 2 double or 2 queen beds.
Here's the number for WDW Resort Reservations: 407-939-7807 (TTY: 407-939-7670) that is listed in the WDW Guidebook for Guests with Disabilities.
They should be able to help with your specific questions.