faux0r
I'm sure you've been trying to come up with a solution regarding your situation with the sibling for a long time, and it must be a very difficult situation with no easy solution, but my opinion is that there has to be some kind of ultimatum so that you can go forward with your life as well.
I'm really careful as I write this as I don't know what your sibling is going through, and I don't mean a single bit of disrespect to your sibling, but is it possible that they won't commit suicide even if you aren't around to help? When faced with the prospect of destitution due to you no longer being available to provide 100% of your sibling's care, do you think there's a chance that your sibling would change and decide to finally take steps to gradually become independent? Since only you know what your sibling is like, you can disregard my comment if it's probable that your sibling will kill self when they're forced with no longer being able to continue their current shut-in lifestyle.
While I realize that people who like their jobs likely won't make posts on Reddit to rave about their respective position, and that a subreddit is likely to attract people who want a place to vent (just as people are more likely to post online reviews about a business given a negative experience rather than a positive one), through reading about realities that many people face, I quickly realize it's not all roses & sunshine on the other side of the grass and each field comes with its own set of frustrating challenges.
What I do is may be a cynical way of looking at things, but especially if you currently have a well-paid, fairly comfortable position, you shouldn't take your current standing for granted, and realize that there are loads of people in other fields who'd rather be in your shoes.