If I purchased the game on steam, and on my switch. Would I be able to use the same account on both of those?

And if I did would my wife be able to play on one while I played on the other in the same game?

Or at the very least would I be able to sign out on one of the devices and have her sign in so that we could both play independently together?

I don't know if I'm wording this properly. I gathered that if I purchased the expansions on one of the platforms that I wouldn't need to purchase them again on another. So I want to be able to play with them on both depending on where I'm at, but I also want to be able to play with my wife and not have to worry about the game not allowing me to be on both devices at the same time. Or not allowing me to sign in to like another user on one of them.