Do not do option C. That will add hours to your trip. Too bad they couldn't get to Flagstaff and leave a car there. That would save you a few hours each way on the way and way back.
Maybe someone here on HB that lives in Flag will let them leave a car out front of their house.
If they drive to Flag not towing, it is only a 2 1/2 hour ride. About 3 towing.