Now, if you haven't yet, now is the time for you to go see the situation in person.  

Personally, I'd go with the As-Is scenario.

We would want to use it for personal use probably one per year. 

Using this method, we will have our home paid off in about 2 more years AND will have a massive HELOC we can use to scale even more. wht are you going to do after the mortgage is paid-off ?

This is so I know if I should keep the person I currently have.

I personally would not invest in detroit as historically its not a appreciating market and for cash flow and I invest primarily for appreciation - I go off the location location location mantra. 

One-person rental units are in the highest demand, and co-living directly appeals to this market.

Tell me - someone selling their home to your son, Subject-To - is this a person who has made good life choices? 

A contract is only as good as the person enforcing it.

While personal loss is difficult and understandable, running a business that directly impacts property owners requires a contingency plan.