You may go through the original lease agreement.
Confirm if the lease agreement was entered between the firm and you (landlord), if so, whether one or both the partners have signed the agreement.
If both the partners have signed the original lease agreement then it is pertinent that both of them have execute a joint agreement with the landlord for the conditions thereon to vacate the premise.
If not then you may ascertain who had signed the original lease agreement and in what capacity, so that you can tackle the tenant on the same line.
If they don't agree with the amicable compromise situation or solution, you may refuse to accept their proposal and issue a legal notice to vacate the premise for default in rental payments and follow it up with further legal procedures to evict them.