Some of them are now owned solely by the widow, and some are owned jointly by the widow and 2 of her adult children. 

There are not a ton of people that live that way and they are typically students or people with little/no money....why else as an adult would you be sharing living space with someone you don't know?

He is experienced in the most profitable industry in our area (cannabis) and works steadily with that, and I do believe he could make the payments with little to no trouble, but his lack of financial "adulting" has me worried.  

She is an adult. 

These are young, able bodied adults and the husband is sitting at home all day.

The 70 year old, could have had kids at 20, the kids could have had kids at HIS 40, so these grandkids could be 30 year old do nothing kid-adults! 

Then you can pick up on certain things like getting bigger 2/1.5 vs a 3/1  because the area you chose is full of young adults who like to go out but don't want to share a bathroom.

We've both rented our entire adult lives and, while we're comfortable with investing in paper assets, we have zero experience with real estate.

As a father of adult boys myself, I can appreciate it.

For example I have a policy of no more than two unrelated adults in a property.