I have stayed several times at the Belize Yacht Club and I believe this would be a perfect place for you and Ma to stay. The grounds are absolutely beautiful and there are solid walkways throughout the resort. Pool, coffee bar, and poolside bar are very short distances from all units. There is a concrete ramp that leads down to the beach and dock. The staff is extremely accommodating. I bet they could make arrangements for a wheel chair and anything else you might need during your stay.
I hope you enjoy your stay in Belize!