I think, when you explain things to people (i.e. in instances where it's not an absence of knowledge that's the problem), the vast majority of people know we're correct, but are held back by convenience. They're embedded into the Google ecosystem or whatever, and it is a pain in the ass to migrate. There are many popular services for which there isn't a 1:1 private alternative. I can openly and confidently say that I sacrifice some convenience for privacy, and to me it is worth it. But other people, while they agree that they don't like being spied on, are used to being spied on and therefore have a "if it ain't broke don't fix it" attitude. They're already using spyware and it's not had an immediately obvious acute consequence for them, so there's not really any turning point at which they would go "this is enough" and change.

I think so long as they're aware, if they do value privacy, over time they should slowly replace the things they use. Also, some of my friends get Signal just to speak to me since I'm not really on anything else (unless they want to email me lol), so that kind of effect may push them in the right direction.

If your brother doesn't care though, he just doesn't care. Privacy is actually very straightforward: it's creepy for someone to be spying on me and watching my every move, therefore I take precautions to make that difficult for people wanting to spy on me. You don't need to convince people that being spied on is creepy. They know that, and are stopped by inertia, which they can only overcome on their own. I don't think it's worth nagging them about it when they already know what is to be known.