BIL is crazy

My boyfriend, his sister, her husband, and her two kids live together in their dad’s house. My bf moved back in to help with the bills when his dad got sick like 5 years ago and couldn’t work. Around the same time his sister’s husband lost his job (due to being stupid) so they moved back in with their dad too. So my bf was working crazy hours to make enough money to provide for everyone since he was the only one with a job. He was also basically raising his nephews because his BIL didn’t have much interest in being a dad. The past few years his BIL has worked on himself enough to where he eventually found a decent job where he could at least take care of his family financially and his dad was finally well enough to be able to go back to work part-time. We got together about a year ago and are expecting a baby next year so we’ve been looking at buying our own house together.

Well BIL went off the deep end again. He quit his job, got back into hard drugs, and is all over the place emotionally. So now my bf is back to working crazy hours to support their family again while he has his breakdown. His sister is kind of in denial about the whole thing and knows she needs to get a job but hasn’t even looked yet. My bf is obviously very upset because he was so over working all the time for other people and looking forward to moving on with his life but now he feels like he can’t.

I barely get to see him anymore because he’s working so much but he’s also constantly low on money because he has to support 4 other people so I’ve been putting back most of the savings for the house and baby so far. And now he’s talking about not moving in with us after baby is born because he doesn’t feel like he can leave his nephews and sister in that environment alone. He’s been really upset about all of this and I don’t know how to help or what to do. It shouldn’t be his problem but it is, neither of us are the kind of people who could just cut them off and let them suffer.