I don't know if there's anything special you can do.. But I wanted to tell you I read, I hear you and I can relate.

My brother once advised me to try to react to things my parents tell me like I would if a little child was saying it, that is, not taking it personally but rather think it's something they say out of lack of experience/understanding. Like when a toddler throws a tantrum. Sometimes, when people get old and maybe dement, it can be a bit the same, and you'll just nod your head and say ahaa, yeah, but just to be polite. I don't know how exactly to explain. I mean, I'm not saying that your parents (or mine) are like small kids or old dement people, just that you can try handling what they say in that way. My brother told me he does that. I find it hard to do myself, though. But then, he hasn't had the same experiences with neglect and abuse that I have.

I don't know if any of this is of any use to you, and surely not in relations to your adult brother. But hopefully, in a few years, you can keep a relationship with your younger brother without dealing with your parents.

Take care