Ignore their attitude (yes it can be hard) and either start with an eviction as they are in violation of their lease for non-payment (the $900 they owe) or simply do not renew their lease. 

Still in the earliest phases but my cost is relatively low so a win/win is high probability.

That said, it could be that the location of your property has some sort of local ordinance that has a 90-day limit, and Airbnb is simply following that.

Wholesaling, when done right, can be a win-win for everyone involved, and my goal is to ensure that happens through transparency and education.

Does anyone know if the fire sprinkler system will be needed if I simply rezone the basement as part of the first unit?

Hopefully their deposit is higher than the damage, but if not, you can document everything and try small claims court, but honestly it is not worth your time as you are unlikely to see the money if you win. 

-Zach Lemaster - CEO Rent To RetirementHere are some past threads that may help your research: https://www.biggerpockets.com/users/ZacharyCole/referenceshttps://www.biggerpockets.com/forums/92/topics/765347-rent-to-retirement-reviewhttps://www.biggerpockets.com/forums/92/topics/1116050-a-huge-win-with-cori-from-rent-to-retirementhttps://www.biggerpockets.com/forums/850/topics/895660-my-first-investment-property-an-out-of-state-dealhttps://www.biggerpockets.com/forums/88/topics/1047543-big-profits-from-new-construction-sfr-build-in-cape-coral-flhttps://www.biggerpockets.com/forums/92/topics/983659-first-investment-property-with-rent-to-retirement?

Turns out in some cases comps were overly optimistic, in others inspections contradicted BPO’s, and in more than a few cases the closing date was so close to submission dates that we simply didn’t have time to do common sense due diligence.

Looked award winning.

And I genuinely believe there can be such a thing as win-win.