The accessible vans have a rear ramp and tie-downs, so the wheelchair or
ecv is rolled on fully assembled, and can be occupied. There are only 3 other passenger seats, so their capacity is 4 guests with the wheelchair occupant riding in their chair.
It has been reported that anyone can use the MV's if they just go to one of the participating resorts' bell desk and request that their smartphone be enabled, whether they're staying at the resort or not. I can't personally vouch for that.