I'm going to play devils advocate.

Ok, I think you're a wonderful person butttt. Who died and said they needed your help? Did sil ask you for help? Sorry, but don't you think this is a bit arrogant.
Every one has the right to blow or save money in the manner they see fit, that's what makes this such a great country. really.
You are absolutely right in saying that you can't fix stupid, so stop trying. Some people are happy the way they are and as long as you're not footing their bill I really do see why it's killing you.
I'm a little sensitive because some one just posted how DVC members are pretty much suckers becasue we did not take our money and invest it instead of purchasing our dvc.
I totally think you did a very smart thing with your windfall but I do hate when people tell me what to do with my money especially if I did not ask them for help.