Enforce Consequences: If the behavior continues and the tenant does not comply with the notice, you may need to start eviction proceedings.

Not sure if they are enforced equally though.

Then after they don't pay the lawsuit, you have to pay more money to try to enforce the judgement.

As far as occupancy limits enforcement does happen but it’s not super common and every case I’ve heard of for enforcement is due to neighbors complaints  typically noise or too many cars.

It's good to stay professional and show sympathy, but it's important you enforce the rules set in the lease agreement.

Has anyone hired attorneys or legal counsel to determine if what these towns are doing is actually legal, when it comes to enforcing STR rules?

First, since they're negotiating over financing, it sounds like there hasn't been a meeting of the minds and there may not be an enforceable contract.Second, like it or not, they need to get (and pay for) professional advice i.e.

Side deals like this story are tough to enforce especially cause you can't call section 8 on them and per your contract with section 8 you are getting paid the contract amount so u can't evict them. 

Have leases so you can enforce them if needed.

It makes it simpler to say no, to enforce something, as you are just "supposedly" working for the landlord and just doing your job.