This will never get old, no matter how much it's become a meme these days

This. Granted practice is extremely important and I promise you these people put in the time and effort, but natural talent is 100% real and surprisingly not acknowledge that much.

Nope, you can get one subscription and add all your kids' accounts onto a family plan and they'll all get online. Depending on how much you want to spend yearly, you'll also get access to a pretty big library of digital games, so that may save you a lot of money in the long run

Mobile games (think like Cookie Clicker or those games where you have to break all the blocks and you start out with 50 and the blocks drop lower after every shot)

PowerWash Simulator

Animal Crossing/Disney Dreamlight Valley/Life sim games

Tetris

Switch is just fine. Tons of kids own them and as long as they're not using it like a Frisbee, it's not going to break with regular use. If your kids can take care of an iPad, they can take care of a Switch. Might be an issue if they like playing it like a Game Boy, but they can easily share. Speaking of which, you mentioned might needing a new TV. As long as it has an HDMI connection (and I can't imagine any TV existing from any relatively recent year not having one), any console will connect. But in your eldest's defense, the Switch's cool feature is not needing a TV since you can play it like a Game Boy or prop it up and disconnect the controllers so it's like you have a tiny, personal TV.

Every console you can buy right now allows for multiple user accounts.

There is no "offline version" of a console and every console requires an online subscription to play multiplayer online. There are some exceptions for things like Fortnite I believe, but that's another cost to consider.

Having a disc/discless console is pure preference. As someone who likes collecting games and having the option to sell them, I would never buy a discless console, but lots of people prefer only downloading games, so ask your kids.

If you have a controller for your PC, I'd highly recommend emulators for old consoles. You should be able to comfortably play PS1 and below given your PC. Older indie titles should also be fine. If you want to get into rhythm games (and also improve your mouse aim for MOBAs), Osu is free and beginner/potato friendly.