Rescinding a lease renewal

I’m helping my elderly parents to manage their rental property. Last month, a new tenant family (less than a year at the property) re-signed the lease which is to start at the beginning of October. However recently they have been giving problems for which we actually don’t want to offer another year and ideally we would like these tenants to leave at the end of this year’s lease.

As some background, the single family home has been thus far rented out for the past 9 years twice and is maintained in pristine condition — we actually live across the street from the rental home. We use a management company and everything is fixed on time and maintained with yearly inspections. The second time we rented the house, a young moved in more than a year ago or so with several roommates. Lease was agreed upon and signed. When it came time for renewal of the lease, the roommates ended moving away and this young adult had his mother and adult sister move in with a dog. Fast forward to when this mother moves in. Left and right we get complaints about new problems with the house, but still we fix everything in a timely manner. Once when we went to fix things we saw the well kept carpets were ruined with dog poop and piss. Yesterday, all of a sudden I receive an email stating that there are issues with the AC in the house. In the tenants email she states that she and her family can’t breathe and we are liable for a hotel for her to stay, medical bills, vet bills, and the like.

“If we're expected to go over the weekend with out ac serviced then. We're going to have to talk about reimbursement for the hotel, the vet visits the cut into out paychecks for missing work from lack of sleep, kids missing school. Everyone in the house is starting to develop breathing issues(pets included).”

I am a renter/tenant myself and I understand the need for AC and I understand things can break at any time, but I would never threaten anyone like this. I am also a doctor and I know that people or pets don’t develop breathing issues because of lack of AC. These family is obviously imaginative and litigious. Obviously we’ll fix any issues with the AC, but with this family its one problem after another, none of which have been noted during the inspections. We’ve had two other tenant families in the past 9 years and the number of complaints by both combined were less than the amount from this family in one year. My parents are 70 and 80 respectively and this is causing them a lot of stress given the aggressive nature of these emails. They already have the house paid for and at the end of the day, we’d rather not deal with litigious tenants like these. It is less than 30 days until the new lease goes into effect. How can make sure these tenants are gone by the end of this lease term?

Thank you in advance for your input.