why havent your replacements moved in yet?
As far as i know, you cant just "void" a contract because your plans have changed --- what would be the point in having a contract. How would you have felt if it had been the other way round, and a day before you were to move in your landlord to be "voided" his side of the contract and said well thats ok cause my plans have changed? you would be holding him to his contract, just as he is doing to you. You dont say why the others havent moved in yet, but surely the best solution is just to find someone else to move in and pay the rent? Again, try reversing it ... what if he had said to you "ive got another flat you can have" and then just didnt present it to you, like you're not presenting the alternate tennants to him?