I'm not sure what you mean to do.
To get from BC to MGM, there is a walking path along the Boardwalk and BC waterway. Or, you can take one of the boats that go between BC, MGM and Epcot. They are wheelchair accessible.
If you are talking about driving to the other parks, parking in the lots and then taking the tram up to the park entrance, your DS will need to get out of the wheelchair and you fold the wheelchair and put it on the tram the way people do with strollers. When you enter the parking lot, tell the CM at the booth and each CM directing traffic that you come to that you have a wheelchair. They save spots at the ends of rows for people with mobbility problems. If you are lucky, you will get a spot at the front of the lot and won't need to use the tram at all.
Almost all the buses are equipped with lifts or ramps and wheelchair tiedowns, so bus transportation is a good option. Especially for MK, where the buses drop you off very close to the entrance. If you drive, you need to park at the TTC, take a tram, then take a boat or monorail to the park entrance.
Monorails are also wheelchair accessible.