Is the son sinful for refusing to hand over the apartment's lease to his father, which the father wishes to reclaim?

If the rent for the apartment is unknown, such as being part of the maintenance costs of the apartment, then the lease is religiously invalid and must be terminated. The landlord is entitled to the fair market rent for the period of occupancy only. However, if the rent is known and the contract is valid, the landlord is not permitted to terminate the contract before the end of the agreed-upon period unless the tenant does not need the apartment and the landlord does.