This says it all: "He has bad hips and has trouble walking long distances." That clearly is a disability. Not only would he not be enjoying himself by being in pain, but it would ruin everyone else's enjoyment of the vacation because (a) he would be in pain, and (b) he (and the group) would have to stop often while he was resting.
An "invisible disability" is still a disability. He knows he has a problem, the others in your group know he has a problem. Whatever anyone else thinks does not matter.
You may be better off renting an
ECV, as pushing a wheelchair can get very tiresome, especially if you are not used to it. There are hills which are not noticeable to people who are walking along, but definitely noticed by people in (or pushing) wheelchairs. Also it depends on the weight of the passenger and the condition of the pusher(s).
Renting from off-site guarantees you will have a wheelchair or ECV always available, and can be useful in the hotels and Downtown Disney as well as in the parks. Some information for off-site rentals are:
Walker Mobility:
1-888-726-6837
www.walkermobility.com
Care Medical:
http://www.caremedicalequipment.com/
Phone (407) 856-2273, Toll Free U.S and Canada (800) 741-2282
RANDY'S Mobility is in Kissimmee
407-892-4777
http://randysmobility.com/
Colonial Medical
http://www.colonialmed.com/about_cms.html
(800)747-0246!
I have used Walker a few times. They will ask for a credit card and charge it the day before arrival. They will deliver the ECV to your hotel bell services before your arrival and pick it up there after your departure. Their rates, especially for longer than a week, are much better than Disney's. Also, their scooters are much better.
You don't say if you are renting a car or what. If you are using a car for getting around, the
ECVs break down into five pieces, the heaviest about 39 pounds. They take about a minute or so to take apart and about two minutes (once you are used to it) to put it together.
Another suggestion is find out your state's requirements for a temporary disabled hang tag and get the paper work and have your doctor sign off on it. The tag will allow you to use any of the handicap parking areas (which will be a necessity). Also, with the policy of charging for valet parking, with a handicap hang tag the fees will be waived. Also the valets will usually volunteer to assist in loading/unloading an ECV. In Virginia I printed the required form from the DMV website. When I took the completed form to the DMV Office it took less than 15 minutes from the time I walked in until I had my tag.