And anyone can use the TREC 20-14 (basic purchase agreement).

I would say don't buy just because you don't even give the most basic info to base a decision on. 

I have done plenty well following some basic real estate investing guidelinesIt's too long to repost how I do that so I'll put it here: It's about the 6th post downhttps://www.biggerpockets.com/forums/311-buying-se...I take the Balou approach from the original Disney movie "Jungle book" "if you act like that bee acts, uuh, uuh, you're working too hard".Set up your Systems & Procedures, Analyze your market, put together a marketing plan, work your market, close the business and Repeat

For absentee owners, cash buyers, & high equity you can pull from Listsource.com or Realquest (basically the same company one is pay as you go the other is subscription based). 

Unfortunately, there is really no best and quickest; it's all going to take time, a lot of reading and some understanding of basic repair.

I'm basically at the end of the rope with him and its time for him to pay the piper

I’m not an expert on real estate or multifamily but I understand the basics and can probably provide some help if it’s on a basic level of simply wanting to own rentals.

You can have him sign the title over to you and basically take it sub2 that way you can control the property and resell.

I'm a little unclear on the actual process of having the interest in these notes assigned.I know it involves an basic assignment of note, having the named-insured on the insurance policy changed, and notifying the borrower of the change.

Basically paying for your place to live.Nothing is set in stone, do things how you feel they need to happen.