Hello Kristy and thanks for bringing such a great question to the Disney Parks Moms Panel.
I can just visualize how excited you are about your dear Dad flying in to be part of the magic of a Walt Disney World Resort family vacation; how fun!
It's easy and convenient for Guests visiting Walt Disney World Resort to utilize either ECV Rentals or Wheelchair Rentals and it's even possible to rent from one of the featured private companies as listed on the previous links.
After paying a refundable deposit ECV or wheelchair rentals through Disney can be arranged per day or for a small saving - for your length of stay (although not during peak times); currently ECVs or wheelchairs cannot be reserved ahead of time and are allotted on a first come, first served basis.
Guests can rent ECVs or wheelchairs at all 4 Disney Theme Parks plus at Downtown Disney; please be sure to have your photo ID to hand! Park hopping is very simple, just keep the receipt and show it to the Cast Member at the next rental location for a replacement mode of transport!
Additionally the use of wheelchairs at Walt Disney World Resort Hotels are complimentary in exchange for a refundable deposit.
If I can help sprinkle any extra pixie dust onto your upcoming Walt Disney World Resort vacation please pop back to ask me another question.
Have a great Disney day.
~ Jane