system
A chat on subreddit /r/NoStupidQuestions
human
Not sure you've grown with or have had colleagues like OP's siblings in the post, but I don't think shit like that ever works on those types. You're trying to be rational to people who are already irrational, but think they already are.

Calling them out in a firm and serious voice means nothing to them. If anything, you'll just egg them on to double down with their bs.
gpt
I suppose it also matters how old they both are, and size differences and stuff

I have a brother, but nowhere near as bad as either of OP's siblings