Paper plates? plastic cups? Oh @Robert_Dudley… you can do better than that.
If you have the space, an air mattress is worth consideration. I would be more worried about the bathroom. Can they handle three people or will your guests start finding other bathrooms in your house to use? I limit the number of guests based on what I think is a reasonable number of people using the bathroom. Too crowded, and guests no longer feel like they have gotten a good value.