Lost

I'd recommend flying into Flagstaff (FLG) if they want to limit driving. American has a major hub in Phoenix with six flights a day to FLG. It's about a 1.5 hour drive Flagstaff-Grand Canyon, and 3-3.5 hours Phoenix-Grand Canyon.

Flagstaff has numerous hotel options, and would also make a good base if they would also like to visit Sedona. Flagstaff is a nice town by itself, too.

Tusayan, AZ is a small town right outside the south entrance that caters to tourists and park employees. There are hotels and basic stores, restaurants, etc catering to tourists. There's also hotels inside the park such as El Tovar, but they may already be booked up for May.

There are several shuttle companies that make trips to the Grand Canyon from Flagstaff and Phoenix. Just Google something like "Flagstaff Grand Canyon shuttle" or "Flagstaff Grand Canyon tours". Arizona Shuttle is the one I see most often. I'm pretty sure Pink Jeep Tours offers trips up there, too. With your friend's medical condition, you'll probably want to call a few if he requires any special assistance. The Park offers a free shuttle bus system to all the major south rim attractions. It operates very similar to a city bus network.