Some people always find a way to make the wrong choice.
It's oh so very painful to watch. Been there. :-(
I feel for you, Chris.
In my mother's case, her worst problem was managing money. (And she remarried a worthless slug of a person, but we shan't go there. ;-) The only way to keep her from mismanaging her finances was to make the decisions for her, or more accurately, prevent her from making financial decisions. After her stroke she ended up in a nursing home, so that part of her pathology finally was put under control.
It's my experience that adults rarely change personality traits or pathologies. It takes some sort of major event to get people to change (myself included), and even then it's easy to revert back to the previous trait or behavior. We're all creatures of habit.
It's easy to see a solution from a distance, but unfortunately, it's often impractical to implement it. In the abstract, someone needs to babysit said SIL and make sure she doesn't make the wrong decisions wrt said WPoS. That, in the abstract, means someone needs to take her and her children in. But I'm sure that's impossible and I'm sure that she wouldn't accept that anyway.
That's the solution I tried with my mother. It lasted less than 2 years and the stress damaged my relationship with her (even more). And in the end, it only delayed her spiral down for a while.
So even if one sees the solution, and tries ones best to implement it, there's only so much a person can do to help someone else. Ultimately, personal responsibility is the most important thing. If it's not there, moving Heaven and Earth won't help. Sometimes support group discussions can help the person, but too often they're impractical to attend. :-(
Hang in there. And best of luck to said SIL and her little ones.
Remember, we don't get to pick our relatives. :-)
Cheers,
Scott.
