Eh, I'm living at home with my mom, no relationship but obviously straight. Its the new normal.
If you actually want to start a business, the question is what do you want to do.
Being self-employed has only one benefit: No Boss. But you're the boss. You gotta tell you to do stuff, or the business falls apart.
So it needs to be something you generally want to do.
Hm, since you have experience in retail, perhaps running your own resale business would be worthwhile? You could pick up stuff at a flea market, clean & repair it, then try to sell the slightly used stuff at a market fair in a more prominent neighborhood.
Or if your current job is great but they're not paying enough, what is your current job? Does it have skills/responsibilities/etc that you could transfer to some self-run business?
...or just get into the legal marijuana retail business. I could never do it, because I get crazy paranoid from marijuana, even to the point where second-hand smoke triggers a mild reaction. But if you are ok around it, its a hugely lucrative business that is being created while we speak.
As for the sibling with kids, remember this rule: More kids = More problems. There is zero equity in children. You can be the crazy rich uncle, because those kids will drive your brother into the poor house, LOL.
Almost 30? Heh, I'm almost 40. You whiny millennials, back when I was Gen Y, we didn't have the Big Bang Theory mainstreaming geekness. We had to cross train geekness with self-defense courses to avoid beatings in school by classmates. And this was mostly before the school shootings, so there was zero security and a lax school administration.
"b-but your soo smart"...yeah, my mom says stuff like that too. It's probably true, the smart part.
...to be honest, if you can't figure out how to start your own business, you shouldn't do it. Starting your own business is only the first hard thing you'll have to figure out if you do start your own business. I often refer to my office as a Mine, where I dig through files for money. Not manual labor, but hard work for modest pay.