Roommates moved in early, which made us pay more rent. What should we do?

This is easy to handle. Even brothers have time to settle accounts. Don't you have electricity and water bills every month? The first month's water and electricity bills are all taken care of by them A and B, which is the latter AA system. But to make it clear in person, the first month's water and electricity bill has come out. Find students a, b, c and have a little meeting. Tell them clearly that you and C bear the rent, and then AB is responsible for utilities or property fees. If the difference is not big, forget it. After all, both you and C have learned how to deal with such problems.