I did find some background on him and it seems like he's been mainly focused on stocks, etc, right?

Home Depot in stock cabinets are just fine for a rental.

That was a bright spot in an otherwise frustrating relationship.Combining your advice, I think I will try and minimize face time (which should inherently minimize conflict), have the yard cleaned up, collect rent (impersonally) and then find a better fit in tenants when they leave (which they will certainly do for work reasons). 

His attorney has suggested we secure the loan with a pledge of stock in his company, but I'm concerned this may come across as a partnership and trigger UBIT.

As the years past, we had all of our money in stocks which we lost a lot in 2008.

Its much like looking at stocks and comparing how well each has done and looking at its 10 year history, like Benjamin Graham taught.

Plus you'd have access to 401k funds to invest in things that return better and less risky returns than the stock market.  

@Getachew Hundera,Another source of private lenders is anyone with whom you establish a personal relationship (prerequisite to private lending per the SEC) who would consider investing in your deal.Essentially, it could be anyone who is nervous about the risk and volatility of the stock or other markets and is looking for a safer investment secured by real property.Learn how to attract and engage private lenders other than your family and your current friends and associates.

Problem is, there are many more sharks than mentors, and they are more interested in draining your $15k than getting you started in the business, and you as a newbie won't necessarily be able to spot this before it is too late.

Our corporate setup is somewhat different than most REI LP or LLC and is more like a Tech Start-up which is heavily scaled to dividends, stock options and long-term recurring revenue.