Any additional due diligence questions or red flags I should look out for. since its my first time to invest in multifamily3.

Was it on yellow paper with red ink?

More secure and stable than an STR (also less competition) but you aren't in the red like you'd be with an LTR. 

Both the daughter and Dad have excellent credit history but feel this is a red flag. 

They city will red tag it and require you to upgrade everything and get a Certificate of Occupancy before you can rent it.

However, years of financial struggles and competition from major players like Walmart, Target, and Amazon contributed to its decline.Following the closure of the Hamptons location, Kmart will have just one downsized store in Miami, Florida.

Amount of money you spend matter (big players spend tens of thousands of dollars per month on marketing).

Heck go to the casino and put it on roulette wheel of black or red. 

MInut has a low average review (mid-3s I think) on Amazon which is a bit of a red flag. 1 per room at a total of $60/month sounds excessive for something that is not likely to be a common occurrence. 

Major red flag for me that they won't give you one.