The shared internet thing is a setting that comes turned on for Xfinity routers by default (aka the ones you rent from them). If you go into the settings of the router you can turn the wifi sharing setting off.

Same here! Good news is that baldurs gate 3 is coming out on August 3rd - not long now!

If you and your wife are into D&D-type stuff Divinity Original Sin 2 has local co-op. It's an isometric turn based adventure game. Super fun to play and on sale for about $18 at the moment, I think. I will say, it's a little more involved than some of the more casual games like Stardew, but if you're willing to put in a little time to learn the game it's one of the most rewarding games I've ever played.

My girlfriend and I actually played through the whole thing together!