I applaud the belief that the older ones are still trainable, but it's clear that they're not going to change and any videos you find will be wasted. Accept that they're happy with the arrangement and they will not spend the necessary intellectual energy to remember anything you show them. They're codependent upon you. Use a little tough love and start cutting them off. Then they'll do one of two things: Learn, or find someone else to be dependent on. Hopefully the former, probably the latter. That 9-year-old will probably inherit the mantle as soon as he/she is ready, and I'm guessing he/she will be a lot more willing to learn from you and you won't need flashy videos.
If you've got the stomach for it, you can do as others have been suggesting and become a jerk when it comes to technical support. Not an in-your-face-I-think-your-an-idiot-jerk, but give enough push-back so that they realize that you're the last option, and not the first option, when something goes wrong. With my own mom I was able to wean her off my tech support by saying (semi)-gently, "You need to learn to do it for yourself." What happened instead is she switched to my younger brother, and when he left home, the next door neighbor. I still end up helping her on holidays, but I no longer get random phone calls to get pictures off her camera when I've never seen her camera before, or her latest computer setup, and she doesn't know how the pictures are being saved to her camera in the first place ("Does it have an SD card?" What? I have a charge cable that goes into the wall, will that help?).
Macs may reduce the spyware, but it's not going to eliminate your problem. I was visiting my grandmother last year who has a Mac and she couldn't figure out why her printer was doing weird things. In the printer tray was a sheet of paper that said, "Your computer has been HaXoRed by...." Grandma calls Apple tech support and loves them. But then she's also got the cash to do that kind of thing.
Don't install Linux or an alternate OS unless you WANT to be the only go-to-guy for tech support. Keep it Windows and the pool of other people to help them is larger. Anyone that embraces the concept of Macs in a Windows world, or the geek-factor of Linux, usually has some desire to learn things on their own, which doesn't sound like your group.