Need advice on my bipolar brother and his young kids

I (27F) need advice on what to do about my brother and his family. My brother (46M) has bipolar disorder and his wife (46F) has cancer and recently developed dementia as a result of the radiation and brain surgery. They have three kids that are under 12 and one of them has autism. They are all obviously in distress but my brother has had a very hard time dealing with this and has gone into full panic mode. They hunkered down completely since the start of 2020 and to this day the kids still haven’t seen another kid or socialized at all. He also will not get them vaccinated so they are stuck inside all the time. On top of that his bipolar can make him get extremely angry over things that don’t make sense. He’s not physically abusive but he yells a lot and can be mean. The worst part is that even before Covid he had started homeschooling the kids and it doesn’t seem like he’s actually doing the schooling. When I visited last year I stayed for two weeks and he didn’t do school with them even once. And I asked one of the kids and they said he forgets a lot. The kids basically spend all day on their phones in their rooms with no structure or schedule or activities or anything. I am highly concerned about the kids having no outside resources other than his parents. And I’m worried about then environment my brother has created for them especially because he goes off his meds all the time. I don’t want to call CPS because I really don’t want those kids ending up in foster care because I know how much abuse exists there too. I’m looking to see if anyone knows of organizations that can help with these kinds of situations. Or just any advice in general.

TL;DR My brother and his wife are medically and mentally unwell and their kids are not in school and I would like advice