Sigh. I'm all for putting family number one. I certainly feel that way myself. However, I have a similar situation with my own mother, who left when I was very young and is now with a man who is pretty much useless. When things have gotten really financially (and otherwise) rough for her and her boyfriend, I have offered to have her come live here. But he was not invited. I've had a rocky at best relationship with her but she is my mother and I will help her and care for her as she becomes elderly because that is what family members do and I want my kids to see that. I don't, however, want them to see living in our house, an alcoholic, refusing to work for no good reason, chronic marijuana user, living off my mother's wages, will steal from you if he gets the chance, no good loser. That would be the boyfriend.
Maybe I missed it, but where if your husband's biological dad? I'm just curious because my dad passed away last year and now that I don't have him, my mother is my only parent and I feel even more strongly that I should take care of her in her old age. She is not a perfect parent by any means, she in fact rarely acts as you would expect one's mother to act. Nevertheless, she is my mother.
Also wanted to say that "taking care of" doesn't mean giving them a ton of money. A place to stay yes, but a contribution towards household expenses or possibly providing childcare while you are working or buying groceries every other week or something, if the person is able to work and/or has some type of income/assistance is not too much to ask.