H Gauss:
The note did have a fair interest rate, 4.08%, compounded annually. (Edit: This was chosen from the IRS minimum interest table at the time to avoid gift tax consequences) As for holding it "until they pass away" the reality is they are much younger than me, there are two of them on the note, and I have a disability. So, while it's possible, it is much more likely that I will go first.
The next issue is the amount. Because of the scope of the financial disaster they were in, I lent them a lot of money. And I've done the math. While doing this did not put me in immediate trouble, should I not get any of the money back, in a timeline as short as 5-10 years my own retirement finances could be in trouble. To give a brief ground on my situation, I am a devoted (20 year member now) FIRE planner who, due to an unexpected disability, was forced into retirement years early. My FIRE planning really saved my bacon! But this loan put me at risk.
The third and final issue was the shock. Although I have given "don't loan to family" advice countless times myself, I never seriously considered, especially since I took steps to secure the loan (due to issue 2) that they would refuse to pay me back. That illusion came crashing through when, sitting over a kitchen table discussing the matter, I was told to my face that they "weren't going to pay me anything because I didn't need it" and "I could go to court if I wanted but I would get nothing." I felt a grave injustice was happening and wasn't going to accept such a flat out refusal.
I immediately called a lawyer. In the painful months that followed I enforced payment followed by selling the loan to a 3rd party bank and getting enough of the money back as a lump some to properly shore up my long term financial projections. I should be good for many more years now.
It was a painful lesson and I still kick myself for lending the money-mother involvement or not. I could have just rented her an apartment or something when they lost the house. Lesson learned. I'll not make that mistake again.