Sharing computer can see other persons character/game

You can't. You always see all local worlds, no matter from which steam account. That's not different for a lot of games, btw - pretty much all the ones that don't have player profiles like Eco.

There was nothing mentioned in regards to that in OP.

That's not what I understand, sorry.
No, Eco cannot be used for Family Share.

I'll be honest: I see totally no benefit in doing that, but wasted development time. If you don't want to play on your wifes world, just don't do it, lol.