Not a Disney trip, but I’m headed to a combo work/fun trip to Phoenix tomorrow for 5 days, and my husband and I have both managed to squeeze both of our stuff into 1 carryon bag + 1 backpack that we’ll share. (He’s recovering from a minor surgery and can’t lift things for the moment, so it’s all on me!)
In the carryon, we have 1 pair of “nice” shoes for each of us, flip flops for each of us, socks stuffed into said shoes, a collared button down shirt for him, 3 casual shirts for him, a pair of shorts for him, bathing suit for him, 5 days of underwear and undershirts for him. I have two casual dresses, a pair of shorts, 4 casual shirts, and a bathing suit + cover up. That all fits in a standard US-size carryon WITHOUT needing to expand-y the zipper.
We’ll also carry on a backpack with both of our toiletries, a hair brush for me, hair straightener, curling iron, belt for him, underthings for me, small homemade first aid kit, plus a laptop and charger, phone charger, headphones, water bottles for both of us, and a small daytime purse for me.
And then he’ll wear a pair of khakis on the plane (which will also work for nicer dinners) and I’ll wear jeans. We’ll both wear comfy shoes and casual jackets in case it gets cold at night.
So I think it’s definitely possible, especially if everyone in your party packs a rolly bag and a backpack. The key is generally being ok with re-using pants/shorts, and really limiting pairs of shoes. Good folding helps too.
My biggest packing “success” story was an 11-day trip to Peru that included both heavy hiking boots plus both warm and cold weather clothes, and all fit into carryons only.