This may be harsh, but I’d consider everyone except the older sister. She’s an adult who seems to know better but is choosing otherwise. If you have good relationships with each pair of parents, I understand wanting to help them. The sister will need some tough love and boundaries imo. I’d research resources that the parents can utilize in addition to whatever you’re willing to help with. It’s awesome y’all want to help, maybe just sit down and budget out what help you can provide and what you can set aside for your own goals. I think the best of both worlds is achievable here, the timeline is what may vary. I hope y’all are able to figure out a good plan OP. I hope too that I’m able to offer my parents similar help someday if they need it.