Holy hell that is confusing.

The entire utility of using a computer to do this is to simplify things. At its current state, I may as well use a piece of paper and a calculator.

I'd recommend setting up some sort of simplified view. The person managing the house can set up all the users and bills that need to be paid, then the other housemates can just see what people are expecting them to pay and make payments accordingly.

I shouldn't have to figure out that I need to pay Mark for the rent, the system should know that I need to pay $200 as my portion of the rent, and that if Mark's already paid $800 for the rent, the $200 should go to him.