You will be fine! I have never had 4 in a cabin (just my DH and me), but I tend to pack "heavy".
I am always amazed with all the closet and drawer/shelf space. Your suitcases will be stowed under your bed.
I do recommend taking extra hangers. I usually do.
If you feel the drawers or shelves are too crowded, leave a few of the clothes in one of the suitcases, until needed.
I can't recall the specific cost of the laudry, but seems like it was 1.25 per wash load. Take a roll or two of quarters and your own laundry soap (in a zip-lock baggie). They also have an iron that is available.