The most economical would be two value rooms. However, I agree with others that it would be most comfortable for each couple to have their own room for privacy. I would not have been comfortable sleeping with my boyfriend feet away from my parents or my sister and her bf. Now that I'm married, I still wouldn't be! Granted, it sounds like you are footing the bill, which is very generous. There is certainly nothing wrong with keeping costs down, but I'm not sure sharing sleeping quarters (and bathrooms) would be comfortable for a group of adult couples.