I've seen a few articles online that reference a Michigan law that restricts investors to selling 4 houses per year - is this actually tracked/enforced?

As I get bigger and busier, perhaps I will enforce that more.  

Interpolating that to this scenario, I can see where I want to learn not just the statutes, etc but how they're enforced in reality in court and that requires a practicing attorney in this specific field, exactly what you're saying as well!

Call you local code enforcement guy or better yet stop by and bring him donuts. 

My understanding is that the 'grandfathering' is only for current owners even though it's supposed to continue, local officials often take the opportunity to enforce rules where they had not before.  

If you don't enforce the rules what rule will they break next.

Know how law enforcement for your jurisdiction does their part for situations where the tenant refuses to leave the premises when required by law to do so.

Set your rules and gently but firmly enforce them.   6.  

Check with your attorney - that might not be enforceable in this case.

They enforced the rules; my relative only lasted for a few days.