Disnee Dad Says.................................At a minimum you will need to do laundry once, and I would go for twice. Do it once and need to pack for 6 days, do it twice and you need to pack for 4 days. Pack a couple smaller carryon luggage, not all big check in types. We are 3 and do not check in baggage on our 8 to 10 day trips.
If you go with two big suitcases, and 3 or 4 smaller ones, you will be able to get by with an intermediate. We always get a compact, even though we could get a sub compact, but they are just too small. With two small ones in the back, you have room for small luggage up front, in the back! If you do laundry twice, you can get by with a compact. Check the prices, sometimes the jump to intermediate from compact is just a couple dollars, other times it's a lot.