ELI5... Share games between 2 devices?

Ok, sorry to ask, but ELI5.... My son has a switch 1 with some physical and digital games. I just ordered a Switch 2.

Am I correct I can use his physical game cartridges to play those games?

Is it possible to share the digital games? Like maybe we both log into each other's switches to share digital games? And each play them, assuming the other is not playing it at the same time? (Like we do on PS5).