I'm not trying to be confrontational, but where I'm from $1,500 for 10 months looks like $15,000.

My personality type is non-confrontational and not one to throw people under the bus in front of their face.Now I decide my next step...I'm not the lawsuit type of guy, and at this point, would want nothing to do with this property under seller-financing terms (he would make my life miserable).Considering asking seller for consideration, or payment, of some sort to avoid going the legal route while also avoiding me dragging this out by clouding title, etc.Definitely not making any quick decisions.

At that point you'd have to decide how you want to confront them or just walk away giving them the stink eye. 

When confronting distrust and lack of resolutionWhat was the outcome of your partnership?

Less chance of confrontation with two young Valley Girl type girls. 

What works: I called the police instead of confronting the squatterWhat works: No police got hurt protecting my property.What didn't work: The squatter.

Meanwhile, the son never bothers to confront me whatsoever.

It's not my job to enforce the law and had I confronted them who knows how that would have ended.To summarize, I honestly think most people are actually better off not carrying due to the training requirements needed.

When confronted with a difficult decision I like to ask myself "If I take action X, what will that look like 5 years from now?" 

may sound confrontational, but just because you might willingly swallow a new pill prescribed by your doctor, that does not mean you should blindly follow advice from your legal team. ( You pay doctors and lawyers, but it is actually up to YOU to do follow the right path.