we stay at a bed and breakfast when we go visit my family. this way we can all visit, but we can unwind at night and have our "special"time AND we dont have to cook or do dishes in the mornings!
sounds like your sister is a bit of a brat. i think you should take the futon and let hubby sleep naked out there! if anyone complains, just say that they wouldnt have to see anything if your sister just gave up the room for you for a few days!