Your brother is a classic example of generationally-created narcissism. He's a male version of your mother.
I also vote for the Cut Direct. I recommend filtering his e-mails to a designated folder and having your DH look at them from time to time just in case you need them for legal purposes.
I also recommend another book on narcissism: Why Is It Always About You? by Sandy Hotchkiss
It has a chapter on "The Aging Narcissist" which is currently relevant (your mother) and will be relevant about your brother eventually. Of the books I've read on this subject this is the only one with such a chapter.
Thank you for the book suggestion. I've heard about it, but I haven't read it before. I will check that out.
"Where to Draw the Line" by Anne Katherine, which is about setting boundaries
"Will I Ever Be Good Enough" by Karyl McBride, which is specifically for daughters of narcissistic mothers
"The Wizard of Oz and Other Narcissists" by Eleanor Payson
It makes sense to me that narcissism is passed down in families. I would think there would be a significant environmental component to that. Undeniably, the children of the narcissist can see and therefore learn from the narcissistic parent's patterns. If the child sees passive-aggression and manipulation, the child may emulate that. If the child sees a scapegoated sibling treated poorly, the child might emulate that. If the child observes indirect communication, the child might emulate that. And if boundaries are routinely squashed in the household, the child might emulate that, too. It would become a pattern in childhood that would continue into adulthood.
I have read that the scapegoated child has a better chance of escaping the bonds of familial narcissism than a golden child.