I don't have personal experience using a wheelchair but from observation there were 2 different processes. One process for people who could walk very short distances was to have them walk on board to their seat (maybe 10-20 steps) and then place their chair with the strollers in a special stroller/chair area Diogo the rode. The on the other end of the ride the chair was brought right to the door of the train for the person.
The other process was for someone completely wheelchair bound and it looked like they took them over to a specific car and loaded them separately.