Assuming you have a copy of the 12 month lease, you can show it to the landlord and insist that the original contract remain in force. The landlord can not change the lease while it is still in effect without the consent of all who signed it. But your roommates are breaching the lease by giving 30 days notice. You have the practical problem that if you sue them for their portion of the rent, etc., they probably have little in the way of assets so you would end up having to pay the entire rent for the remainder of the one year. It probably is better that you insist that if the landlord lets them leave without paying any compensation [entitled to rent until can re-rent the home] he let you do so also. ?Unless the rental agreement made each person liable for a specific share of the rent, you owe all of it.
Answered on Dec 08th, 2016 at 6:04 AM