I say that as the mother of a child, now 17 years old, who has a medical issue where the co-pay is well over $5,000 for just one test. 

I am looking for a duplex to do owner occupied or a house with a mother in law apartment.

They're going to dismiss that as irrelevant, instead offering information about how their wife's mother Susanne is looking to sell her house so she can move to the Palisades, but she hates  realtors because of a bad experience she had many years ago. 

Essentially my father has a multi family home with his wife (not my mother) and his cousin.

Bankruptcy is a real mother for ya. 

But graduate, medical and nursing students will need a place to live off campus come the Fall.

There are also quite a number of these SFHs with finished basement mother-in-law suites so jumping on one of those is not a bad idea either.

Look for the best tenant, nurse working overnight,  single person, etc.

My father went on to kill my mother and himself.

"Mother-in-law" units are just non-licensed duplexes in the eyes of many cities, but here in the Twin Cities they have been loosening restrictions on ADUs.