I thought I finally had myself convinced to go ahead and stay off site for the space and to avoid busses, which I do not like with strollers. We will have a 6 year old, 2 year old, and 1 year old when we go. But then I remembered Pack n plays and car seats, what do you do about that when you are staying off site and renting a car? I know car rental places have car seats, but that again adds to the cost and my husband worked at a car rental place for several years and I saw how they handled those seats, no way would I use them. But there's no way we are lugging 2 car seats, a booster seat, and 2 pack n plays through the airport!
Any timeshare or hotel you'll stay at will have pack'n'plays. Orlando is very kid friendly.
Anyhow, with your young family, its either be patient and wait a few years ...or get lugging.
For the car seat situation, we waited until our 3 kids were all in booster seats before we took a trip featuring a long flight with a rental car, as they are easier to lug. We put the boosters in a duffel bag and carried them on. We also had a stroller we checked right at the gate where you board the plane.
If you don't want to wait and must fly, I would bring two car seats on the plane for your two youngest kids and a booster for your oldest. Your two youngest can sit in the car seats on the plane if you have the right kind of car seats. Then you use the car seats in your rental car. You'll also need a double stroller or two singles. I would bring those also checking them in when you board the aircraft.
We also fly on Southwest, which has free luggage, since you will be wrangling all those kids, seats and strollers you probably don't want any more carry-ons with clothing. With a big family, luggage costs can add up fast!
If you are checking luggage, I would suggest spreading the clothes out so everyone has an outfit in each bag. If they lose a bag, it will probably arrive a day late and by spreading out the clothing everyone will have something fresh to wear for one day.
Or you could forgo all the car seats, booster seats and just take magical express...and buses everywhere.