It looks to me like your brother is more likely in full blown conspiracy theorist mode, which might as well be a psychological disorder (or a symptom thereof), than a mere run of the mill anti-Catholic. If it weren’t Vatican-Illuminati, Jesuit oaths and the like then he’d be blathering on about 9/11 Trutherism, Flat Eartherism, Big Pharma Skepticism, etc.
These aren’t mutually exclusive either! Many years ago I would spend hours investigating these bizarre ideas (it all started with the 9/11 Truth Movement) and making rebuttals for them. I’d actively engage conspiracy theorists both online and in real life. I’ve never once succeeded in convincing a single person to give up their pet theories. In fact what I usually observed is that a conspiracy theorist
starts with a pet theory and before you know it the propensity to believe this kind of whacky stuff makes them susceptible to believing
other conspiracy theories.
One of my aunts is like this. She started with “skepticism” of science/medical organizations. She’d question the safety of GMOs, processed food, vaccines, etc. It started off as healthy skepticism, and as a molecular biologist myself I made sure to answer all her questions at Thanksgiving. Each year she’d go deeper and deeper down the rabbit hole until one Thanksgiving she was in full blown anti-Monsanto/Big Pharma is poisoning us with GMOs and vaccines territory. Then it was the government is poisoning us with water fluoridation. Now a few years later she’s posting 9/11 truther, Moon-landing hoax, JFK-assassination, Masonic/Vatican/Illuminati, you name it she buys it, stuff on Facebook.
I finally realized it isn’t good for my own state of mind to keep debunking her nonsense so I just completely disengaged. I don’t respond to her posts anymore. I don’t spend hours digging up facts for her that she’ll just ignore, or forget about in a couple hours when she gets distracted with her next YouTube chew toy. I don’t hate my aunt. I have immense pity on her because I frankly believe she is
sick. Her whole thinking pattern is messed up such that she’s living in an entirely different reality.
Now you may want to disregard this and try to debunk everything your brother sends your way but I guarantee you you’ll get very tired of this. It will do a number on your own mental health and once you get to that point I hope you’ll take my advice and just let it go. When he starts going on about this stuff change the subject. If he’s incapable of doing so, walk away and don’t engage him.