contract changed after deposit paid

Hi, Could someone shed some light on this for me please? A joint contract was signed (that a copy of was never provided), and a deposit paid. over a period of a few months the people who signed the contract changed. over a month's notice was given that due to these changes they would not be moving in.
And attempts to re-advertise the room were made.
The landlord is now saying that as no one has filled that room that they still need to pay for the room, and threats have been made about collecting the payment.

Is this legal?

Certainly. The tenants signed a contract that they would accept the unit and make the lease payments. They failed to fulfill that contract. How much notice they gave is immaterial unless it was a month to month agreement. A lease cannot be broken by merelyu giving 30 days of notice.

The LL made attempts to find another tenant to take over and minimize any loss of income, to no avail. Since the LL was unable to receive any income from another tenant for this period, the original signers are still responsible for the contract. If those signers were on the same lease or agreement, they are seperately and jointly liable, meaning each of them is liable and obligated for the entire lease amount and that the LL is free to pursue any of them in court for the amount due.

Unless they signed a month to month agreement instead of a lease, they are still responsible and need to pay the rent. In some states, they can be held responsible until the lease ends or another renter is found. (please list a state.) He can sue in small claims court, obtain a judgement for unpaid rent, file liens against personal property, attach bank accounts, garnish wages, or turn the amount over to a collection agency.

A lease is a legal contract. A signer shouldn't take it lightly, it is a legal debt.