Did OP every come back with an update? I'm wondering if they considered just buying the home, as an investment. That way, they ultimately would get the money back. Versus paying the mortgage and risking them still losing it eventually, or having it go to other relatives after they pass on.

I think some boomers who are poor in retirement didn’t necessarily have bad things “happen” to them but had their heads in the sand and just assumed the good times would continue to roll and that they’d be “taken care of” in retirement. My mom is one of these. My parents divorced in their 50s and each came away with several hundred thousand and could have been fine had they just stuck to working and saving for a few more years. My dad kept up working and saving and is fine. My mom made a series of horrible and/or impulsive choices and really made her bed in terms of having no money in retirement. Considering she was not a great parent to me, I do not feel compelled to help her, save for doing whatever I have to minimally to keep her off the streets.

OP there is NO WAY you should feel compelled to help keep your in laws in their house. They need to downsize. Your and your children’s future are depending on it.