Even with vetting guests, they still sometimes break the rules and bring large dogs or have parties. 

He is waiting to be transferred into a nursing home.

Should this not occur, we will use our backup plan of BRRRR’ing (Buy Rehab Rent Refinance Repeat) the property and holding onto it as a rental unit, creating monthly cash flow which can then be reinvested into future and current projects.

I posted here because it all sounds fine and dandy if that's how it all works, but I would imagine there must be more nuance to it that I am not taking into consideration. 

Reading up on Montgomery County, MD but can't definitely tell - When does a house hack fall into an ADU? 

We are now moving into our second home and renting out our first property.

That isn’t the easiest / safest first foray into real estate ownership.

I’m also curious if it's possible to convert these units into regular apartments, as this property is located in the NY suburbs.

I've ran into groups of mountain bikers from Colorado Springs for example in winter months here.Don't forget that "vacation" isn't the only reason people travel. 

Would it be braindead to turn them into tenants or should we go ahead and evict them?