On an average family vacation, my family of four uses two 26" expandable suitcases. However, Disney is not an average vacation
We find we NEED an extra piece for all our Disney stuff (WDW Mist Fans, Mickey spinning Fans, autograph books, pin lanyards, sun hats, etc... ). I take a 30" rolling duffel that never leaves home full but returns bursting!

It starts off with the Disney must have stuff listed above plus our shoes and toiletries. On the return it's stuffed with refillable mugs, cups from restaurants, slushie cups from Goofy's Candy Co, and too many must have souvenirs.
I would make sure you have PLENTY of available space to bring home items from your trip. You don't want to pay expensive shipping fees ($60 to ship a train set home one year!

) or overweight luggage fees trying to stuff everything in to your suitcase.
I also don't mind doing laundry while the family is at the pool either. But honestly it's not our clothing taking up the luggage space!
In my carry on (which is a disney totebag from the resort) I just keep the necessities we'll need for the flight (snacks, coloring books, shorts to change into once we land. I also pack Clorox wipes (have to wipe down the remote control, door knobs and stuff in the room), plenty of hand wipes, etc... For our documents and my stuff I use a small crossbody bag.
Have a wonderful trip!
I have got to finish packing!
