Thank you for the reply.

From my understanding, an agreement should be made between the tenant and sublessee.

I'm the landlord. Do I need to sign a contract with the sublessee? If so, what would I need to include in the contract.

My intent was to sign a letter with the sublessor (tenant), stating that they are aware of a sublessee living there, but that they are still responsible for the terms of the contract, if the sublessee violates the original lease contract.