So let's make it extreme... lets say you have a family of 10 using 5 bedrooms and a family of 2 using 1 bedroom (in a 6 bedroom house). Both families should pay the same? Use the same number of kids... should the family with 1 kid pay the same as the family with 10 kids (just an example)?
Should we break out the restaurant question where two couples go to dinner, one has appetizer, drink, steaks, and desert, and the other couple has soup, salad, and water? I'm guessing those couples should split the check evenly too.