If they do decide to move I would remind the landlord that they are only moving because the relative is moving in and they’d hate for their to be a crime committed by anyone else moving or the property being listed for rent anywhere. 

It reminds me a little bit too much of Ron LeGrand and Russ Whitney.

Talk to others about your meetup and tell them you will remind them.

Said the main cause of the issue was a clogged up air filter (I know, my bad for not reminding my tenant about the importance of regularly changing filters (it's written in the lease that he must replace them every 3 months and that I'm not responsible for bills resulting in replacing filters)). 

This happens A LOT to new buyers. i would remind them 30 days before the rental contracts expire. 

It is just expected - they get reminders a day in advance from YourPorter but they also have access to the cleaning calendar for 30 days out as well.  

I sent them a text and reminded them that our lease states they need to pay on apartments.com and I will not be accepting payments any other way this time.

It reminds me of that viral meme interview:"Sir, what will you do if you win the lottery?""

And you can remind them of that and that most likely the insurance would deny the claim because the wrong party purchased it.

I will be adding this little reminder to my notes of things to look out for when choosing a broker.