'Roommate agreement' kills fraud

Rent it Right

Q: My son and a couple decided to rent a two-bedroom townhouse. Last month, all three signed the lease, and they each put up one-third of the deposit and one-third of the first month’s rent. Now the couple (who share a room) are saying that my son has to pay half the rent because he has his own room. This is not what they originally agreed to among themselves. I believe that since all three are on the lease, they should each pay one-third of the rent. Is my conclusion legally correct? –Jaci J.