Which skills should a player focus on?

[Kethus]

So far looks like Roguery and Trade only increase stuff for the party leader. What about smithing, can you have your companion make weapons?

 

[Iraeis]

you can use your companions stamina to perform smithing actions by clicking on your own portrait in the smithing menu. I'm not sure if the parts they discover are lumped together with the ones you do, though.