I want to give them a chance to provide a fair resolution and improve the work before I terminate the contract & fire them.  

According to her, because the tenants pay their rent by the 1st of the month, if I were to hand deliver the 30-day termination of tenancy notice on October 18th, the soonest the tenants would be required to vacate the premises would be November 30th.  

i would review your contract and see what it says about terminating the relationship.as others said about theirs - with my rentals, i try to price just under market, and i allow pets. 

Since the landlord didn't lose any rent and there were no damages, I can't see any way this would hold up.If your lease is the standard TAR lease (I'm guessing it's not), there is a clause which deals with early termination.

If we determine that your dwelling should not be occupied because of damage or risk to property, health, or safety, we may, at our option, terminate this lease. 

If the tenant terminates the lease, you may be required to give some of the money back.

If tenant has complaint, point to the lease, that they agreed to this utility cost, and indicate they can terminate their tenancy at the end of the lease.Good luck

Make sure it explicitly explains the process for termination if you are unhappy with their services, especially if they violate the terms of your agreement.3.

This is a fairly common situation.On whether you should "let him go" or not, the question is, are you going to hold him to the terms of your lease regarding early termination or release him without further rent or early termination obligation. 

It might be grounds for termination of the lease.Personally if I saw the condition was that bad I would try to negotiate an early lease termination.