My parents (73) want to kick my brother (45) and his family out of their house

My brother and his wife are both medical missionaries. They have spent the bulk of the last 11 years in Africa through a Christian program that places them in understaffed hospitals. They get a monthly stipend, funded by charitable donations, for living expenses. They have two kids, now 8 and 14.
From one perspective, they have put themselves through tremendous hardships to help those most in need. They have lived in rural housing without flushing toilets, home-schooled their kids while working in understaffed hospitals dealing with horrific diseases without modern medical equipment. They have built up a small church community in rural Africa from virtually nothing. And they've likely meaningfully touched more lives than most of us could ever dream of.
From another perspective, they are now in their mid-40s and they don't have a penny to their name. Nothing for the kids' college or their retirement. They live in my parents' basement when they are in the US, which they have been for about half the time the last 4-5 years. They don't pay for groceries or utilities.
My parents recently shared with me that they are kicking them out. When they're here in the US, they don't work, saying that nobody wants to hire a doctor for just a year (and that it would be sinful for them to deceive them). They instead sit around the house and continue their homeschooling of the kids. They won't say as much, but I'm pretty sure their retirement plan is inheritance, though it's hard to say whether that will be a sufficient amount.
My parents shared with me that they do not really want to kick them out. What they want is for them to both get jobs, to put their kids in the local public school, and to start to balance their faith with reality. My parents say they don't even care about them living in the house and not contributing financially, if they would just start earning and saving some money for the future.
My parents are begging me to help convince him to change his ways. I've tried in years past to talk to them about money, but the conversation turns to the true riches of the kingdom of heaven and we get nowhere. When I ask about funding for college they say God will show them the right path when the time comes. It's like we don't even speak the same language.
My mother is increasingly stressed and she tells me she is barely sleeping. She threatened to sell the house and downsize to somewhere my brother and family wouldn't be able to fit, but my brother talked her out of it (and she was bluffing anyway, she's lived in that house for decades and she doesn't want to move). She yells at him about the damage to her dishes and her furniture from his kids, but he dismisses any concerns with material possessions as trivial and meaningless.
I really want to help my parents, but I haven't the slightest clue how. My brother and his wife won't listen to us. What do you think I and my parents should do?
TL;DR: Failure-to-launch brother and his family are saving the world but not a penny for themselves. My mother wants them to either move out or get jobs, but they refuse, and are in an increasingly awkward stand-off.


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