I'd say number 2. The airline (Southwest?) should provide the wheelchair, if he doesn't have one. The only problem I see is having to probably check in at the airport. Maybe that is not a problem.

You call the airline and arrange for it at each airport on the journey.

Renting a wheelchair is probably not a good idea. The place that rents them would probably not allow it for air travel.

A good cheap chair can be had for $300, sometimes less, often more. If he did that it would be his own chair. Here's an example: Just Quickie Wheelchairs