Car seats for vacation

We are going to the Keys for vacation next month. We will be renting a minivan at the airport to drive to our hotel. We are staying at a resort, so we won't really use the car again, except to drive one day down to Key West, then back to the airport.

I have 4 kids, 8, 6, 4, and 4. They all currently sit in Radians in our cars. My 8 year old, is small and skinny and still fits the Radian 100 (i think thats the one we have) She uses it either way. My 6 year old is also small and skinny and he uses it either way, but with way more growing room. The 4 year olds are more average height, I think 30 and 50%, but also skinny.

There is no way to lug those heavy seats on the trip. There are just not enough arms and bodies to move them and the children. In the past, we have rented car seats on the other end, but with them all getting older, I wonder if it is cheaper and easier to just buy some boosters to carry with us.

All of that to say, can I booster all of them for this trip and for future trips? They all fit fine in their radians, so I will just keep them in those for home even though I know they are old enough to be boostered.

What boosters are less expensive, would work well for them, and won't be impossible to carry 4 of them and 4 kids and luggage?

Thanks for your help

How four year old are the four year olds? Are they nearing on to five? I'd feel ok with 4.5 year olds or older in boosters for the first time on a trip, but just four, no. The six and eight year olds you could get backless boosters for.

I'd probably get Harmony Lite Riders for the older two, and bring the Radians for the younger two.

Are the older two over 40 pounds? Or at least 35, given their age? If so, they should fit on the lap belts on the plane.

Wendy