A few years ago, I installed Linux on my parents' desktop (dual-boot)[0] and told them that they were "forbidden" to use any other computer for web browsing, document editing, etc. I told them that this would be more secure, and that's all it took to convince them.
I figured that, this way, at least I could fix any of their computer problems remotely (over ssh), instead of helping with Windows on the phone.
It's been 2 or 3 years now, and they've had zero problems. I haven't even needed to ssh in except to do periodic software updates (which, even then, are superfluous for their purposes).
[0] My dad's work requires some very specific Windows-only software