Realms of Arkania: Blade of Destiny

I've recently started playing this game and right in the first dungeon (2nd floor) I was stumped by two locked doors and a locked chest. All regular methods (foreman and force) of opening them failed so I have only two options left: One is to try and pick them, but I have no picks and I didn't see any store that sells them. The second is to use the golden key I found after defeating a particularly large band of brigands. The thing is, I don't know HOW to use a key! I tried putting it in the left or right hand of the leftmost character but nothing happens - when I try to open the doors or chest I still get the same answer as before.

Help! How can I advance in this game?