I think the cheapest thing would be to rent a large car or van or SUV, something big enough to hold all 5 of you, plus your luggage.
There is also the option of using Disney's transfers, not sure of the price though!
Hope this helps with your planning
P.S. My DH hates to drive while on vacation so we'll be hiring a limo service to take us from MCO to the Radisson at the port (flying in the day before), then picking us up at the port and taking us to the Polynesian, then driving us back to MCO.
With these 3 "legs" of the trip, the cost for using a stretch limo for each leg is $385 PLUS 20% tip. To use a large 10-12 passenger van (including driver) it's $245 PLUS tip. Since I hate to spend so much money for the limo, I'm considering breaking it up and using the van to and from MCO, and using the stretch limo from the port to the Polynesian (since this leg of the trip is the longest) for $290. PLUS tip. Doing this will save us money, but we'll still have the fun of being in a limo after the cruise
As of now, DH wants the limo for the entire trip
He works hard all year, so I'm not going to make a big deal out of this.