I believe a spouse is protected but I don’t know about a child. My suggestion would be to have them get married. Their sex is no longer a concern and so what if it’s a little incestuos, who are we to decide who can and can’t marry?
They managed to scrape together enough cash to acquire this little place and make it livable. Their current combined incomes are sufficient for a reasonably pleasant existence, no extras, no vacations, one old car between them but they make it work. It wouldn’t work with a house payment or rent. My aunt is retired, my cousin has ended up working at Walmart, that’s the only job she could find and keep. Everything else kept coming out from under her and so there they are, holding it together but barely.