Had a couple in the cabin next to us a few years ago who checked the only two bags they had because they didn't want to lug around a backpack or a carry on. Turns out all of there clothes were in one big 32 inch bag and other stuff in a smaller suite case. 10:00pm the first night I hear shouting in the hall. Long story short they ended up buying a bunch of clothes on the ship....
To say they were the most unhappy people during the cruise was an understatement. They even had their meds in the lost bag.
My advice is two bring a carry on and a small back pack for each person, cross pack them. Other stuff goes in checked bags. We can go a week for what we bring in them.