Welcome to disABILITIES.
here's the info that mhopset mentioned about outside places to rent wheelchairs or
ecvs (motorized scooters):
Care Medical:
http://www.caremedicalequipment.com/
Walker Mobility:
1-888-726-6837
www.walkermobility.com
RANDY'S Mobility is in Kissimmee 407-892-4777
http://randysmobility.com/
Colonial Medical
http://www.colonialmed.com/about_cms.html
And a
link to the DIS page about wheelchair touring.
You didn't say which DVC resort is your home resort, but you might want to look at one other than your home resort. OKW is a nice resort to go to with older people. It is spread out, but there are a lot of bus stops, so you would be close to the bus stop wherever you stay. There is a nice large balcony for each unit with a table big enough to easily seat 4 people for breakfast or a cup of coffee. Our home resort is OKW and most of the time, we are staying there with my 70+ in laws. Sitting on the balcony and watching the birds (or the golfers, depending on where your room is) while we have coffee is just a nice start to our morning. One of our "traditions" that MIL and FIL really enjoy is renting a pontoon boat and taking a boat ride toward DD and PO. It's a very relaxing resort. If you rent a wheelchair or
ecv, most of the buses are wheelchair accessible.
BWV is nice because you are close to Epcot and MGM. VWL is nice because it is close to MK, but if you don't plan to spend a lot of time at MK, that wouldn't really be an advantage to you. Transportation to get to the other parks from there isn't as easy.
You can usually get a wheelchair at your resort, but you can't reserve them ahead of time. you also get what they have, so if you need a regular size and all they have left is wide, that's what you get. Some people report that they were charged a $250 deposit that is refunded when you return the chair. The DIS page link that I gave you above has information about renting at the parks.
If you think of any more questions, just ask.