> You download the roms for the local multiplayer but everyone plays them remotely on different clients, and the dolphin software makes it act like its in person local co-op on the same device???

Yeah, that's essentially what dolphin does. You need to make sure that the clients are all the same version. And that everyone has the same save file, I believe. Everyone connects via a code given by the traversal server, but I believe it's still peer to peer.

So the players need to be relatively close geographically. For non-serious games I (east coast) can play as far as the midwest or so. But for good connections for competitive games, I have to stick to east coast.

> with a third column that sometimes your friends come over and play on the same screen

Before covid19 this is primarily how we would play mario party. It's definitely more fun in person, but still fun in zoom.