Buying the duplex next door

[Jeff Kosmicki]

A little history...  In May of 2015 we bought our first home, a duplex that was a foreclosure with a 203k loan. We did some rehab and we are all in for 120k. We live in one side and have the other rented for $765. Based on comps in the area I believe the property value is between 145-155k

Yesterday the son of the owner of an identical duplex next door approached me to see if I would be interested in buying their mothers property, as she was in poor health. The property needs about 18k in repairs. There is also a mortgage on the property. The current tenants are her family. One of which will be moving out soon and the other maybe open to staying.

My question is, how do I buy this property? I have good credit, but not much in the way of down payment. They maybe open to owner finance but how do we get around due on sale? Would there be a way to leverage my property for money down?