I wouldn't spend a lot of money or time on this unless it becomes an ongoing problem.For me the bigger concern would be the lack of a meter for common area expenses.  

We are not worried about any shady dealings, but I am concerned that we do things correctly. 

Not sure what the issue is with COVID...are you concerned that residents will squat and not leave? 

As far as your other concerns, maybe you should ask the town for the permit history. 

John, I own a mold remediation company so to CYA let me preface this with a " if you have concerns you should hire a professional certified and/or licensed in mold remediation." 

Another concern might be if we use up all of the water from the stream which won't happen. 

I was actually much more focused on and concerned about myself getting into trouble for knowingly allowing too many people to reside in the unit.You are correct, the real reason I need them out is to renovate.

With it being an unpermitted duplex that'd concern me too. 45K cash can be used in many different ways.

Any other concerns with this approach I should know about? 

I have a few concerns I was hoping someone could shed some light on.