Oh also as a side note - we were recently on Symphony as well from Miami and my parents used wheelchairs there. The process had a lot of differences which I think is because the Port of Miami has a lot more people hired to push wheelchairs and the waiting was all done indoors. Be sure to keep in mind the time of year you are going because if they are waiting outside for a long time it can get pretty hot or pretty cold sometimes (like it was for us today).
Edit to Add: Once you are on the ship it can be a little while before the rooms open up. Usually around 1:30pm. If you think it maybe a struggle to get them to the room you may want to consider having them stay close to Bolero’s until the rooms open up. Then if the wheelchair is in the room you can maybe go up and get it then bring it back down for use. I know it’s not ideal. If you’re all hungry you could grab food from the buffet, Cafe Promenade, El Loco Fresh, or Playmakers that day and you can bring any of it back to them wherever they are on the ship. It was also nice for my mom that the ship is really pretty short from end to end. We had been on Symphony which was HUGE and she was very surprised when I told her “okay we are at the very end of the ship now”. It made things so much easier for using her cane.