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.