They do have wheelchair accessible vans, but they can sometimes be hard to reserve, since they are limited. They can only accomodate one wheelchair.
If it possible for the two guests using the scooters to step up into a van, and for someone to load the scooters into the back of the van, that might be an option. Not a great one, I suspect.
There's a chance you might be able to call a Mears Shuttle van, and arrange it that way.
Here are two numbers to call in advance, to find out what options they have:
Checker Cab, operated by Mears - (407) 422-2222
Mears Motor Shuttle - (407) 423-5566
On a side note, I am sure there are plenty of other car services out there that might be able to handle your request. Because they would be called by you, and scheduled in advance, they ARE allowed to pick up on property.
I'm going to PM you with one other idea.