Worried about the financial cliff my older brother will hit when our parents pass. How to handle the guilt and logistics?

I (40s M, American) am looking for some perspective on a family situation that is starting to feel like a slow-moving train wreck.

I have an older brother (mid-50s) who has struggled with stability most of his life. He’s married with almost all kids out of the house. His wife has a regular 9-5 but my brother has cycled through various odd jobs. He's had more long term stable jobs but for the last 2 years he's self-employed selling a niche snack food at local events. It’s physically demanding work with very low margins, and I honestly don't know how they make ends meet.

For the last decade, he has lived in a secondary family property owned by our parents (both in their early 80s) rent-free. Despite this massive advantage, he’s broke. He recently had to take a significant advance on his inheritance to pay off five figures of credit card debt. He spends most of his time smoking, numbing himself with weed, dealing with a short fuse/moodiness, and keeping the 24-hour news cycle running in the background.

My parents are finalizing their will and the future of the family land. This has brought everything to the surface. I’ve worked hard my whole life—nights, weekends, and putting myself through school to have a good career. My spouse also has a great career and we are very stable.

I feel an immense amount of survivor’s guilt. I feel gross even talking about his misfortune with my other siblings, but I’m worried about what happens when my parents pass in 10-15 years. His safety net will vanish. I don't want to be his landlord or his bank, but the thought of my oldest brother being destitute is both heartbreaking and embarrassing. Like he'll talk about his work and you're just thinking, this is a hobby and you're not being the responsible person you're capable of being (or maybe once was). He's not incapable but he's chosen this life.

The Will: How can my parents structure an inheritance for someone who is clearly bad with money so it doesn't just vanish into debt?

The Guilt: How do I stop feeling like my success is an indictment of his failure?

The Cliff: Has anyone dealt with a sibling who is aging into a manual labor job with zero retirement? How do you set boundaries now before the crisis hits?