Travelbug:
I'm glad I could be of some help.
At POFQ, they have the bikes to rent that several people can ride (like a carriage bike with a canopy), so that is another way to bike easily-no balancing and not everyone has to pedal!
I should also mention that we took my 78 yr. old m-i-law at the beginning of December. She has diabetes, and we needed a wheelchair for the parks. We stayed at the Boardwalk, as we had just bought into the vacation club. I know you were concentrating on moderates, but Boardwalk is also great because you don't have to hassle with the buses and wheelchairs when going to Epcot and MGM. The wheelchairs go amazingly well onto the boats.
We ended up renting a wheelchair from an outside service-member services at the resort can help you with that if you call them ahead of time and get the number of this medical supply place and place an order for the wheelchair. They delivered a wheelchair to the resort, we picked it up and had it for all week and it was real reasonable-I'm thinking $25 or less for the whole week-and it was clean and new-and then they picked it up after we left (who knows-maybe they keep a stash at each resort).
It was nice to have it at the resort, as some of the walking from the bus to the front of the park (where many people get wheelchairs) can be far, and then we didn't have to hassle with waiting in line to get a wheelchair. I would highly recommend it. As far as getting on the buses with it, my m-i=l would get on the bus without the wheelchair, and my husband just folded it up and carried it on like a stroller so she wouldn't have to go up on the bus "ramp", which makes a rather big spectacle of things.
It was so wonderful getting on the rides and things-the CM just helped us so much when they saw us coming with the wheelchair to get on the rides/shows. It made it so enjoyable for my m-i-l, because she didn't want to be a burden to anybody (she is mobile, but not for very far)-she thought with her in the wheelchair, we'd have to wait in the back of the line and things like that, but we wound up getting good seats on all the shows and rides, and we joked around telling her we would bring her more often, because the wheelchair allowed us to have VIP services!!
But, my point is that the CM don't make you feel like you are a burden just because you have a wheelchair.
Also, take a cushion or a pad to put on the wheelchair seat. My m-i-l's tush got a little tired towards the end of the day, sitting on the seat, and we wound up taking a cushion off the dining room chair from our room (it was one of those tie-on type cushions) and using it on the wheelchair, and she was much more comfortable. But, it would have been nice to a real cushy type pad for her.
Your parents are going to love it!