I have also seen LL with one meter bill tenants based on percentage - I guess I do that in one of mine too (3/1 house with 1/1 mother-in-law apartment: 3/1 pays 75% and I pay 1/1 25% and include internet for 3/1 if they cover 1/2 bill).

I would shovel their sidewalk for no other reason than they were my mothers age.

I found out that there was a messy situation between tenants on the third floor (two young women, on is a mother of a two years old.

With the proceeds from the sale we are going to invest in my mother-in-law's current rentals and expand from there.  

If not, the next best option would be to buy a SFH with some sort of casita or mother in law suite that could be rented on a short term basis (AirBnb/VRBO).

My wife lost her father and step mother within about a year of each other.You may want to talk with a CPA about any tax obligations that may result from your inheritance. 

Mother's house also isn't an investment. 

When digging deeper, I found out that the owner has his Mother renting the unit for around $650/month.

He declined, saying his mother in law had helped them out with some rent money.

Her mother, sister, 3 children, her wife, and her wife's 3 children.