OK - here is a suggestion
Rent a small car for two days -
The day you arrive and the day you leave - one way rentals in the Orlando area are much much cheaper than anywhere else.
That way you don't have to worry about putting EVERYONE on the same vehicle -AND dealing with luggage.
OR just have a couple people take a cab to the resort - and back to the airport - OR depending on where you are staying have some folks take the LYNX bus from the airport. OR does your resort have an Airport Shuttle? You could still rent a car to haul some people and luggage - but divide them to enable you to rent a much more manageable vehicle.
If you rent a 16 passenger van that you are only going to need for the trip FROM and back TO the Airport. You are going to have to drive that monster throughout your vacation - and always worry about parking the beast.
Other than that advice - I have two words....
MAGICAL EXPRESS! HAHA
It really is a life/time/money saver!
We use it every time we fly.
On our last trip we rented a car for one day to go to Mass on Sunday.
But other than that - we rely on WDW Transportation System a lot.
Depending on where you are staying - some hotels have car rental locations right in the resort - a few in the Downtown Disney Hotel District have them - I know there is an Enterprise and an
Avis.