If starting talk with npc all characters, set to walk together within 20m, should automatically participate in it. With this setting we should get all special dialog options (eg. race) from whole teem, and actions like persuade/intimidate/etc should be performed by character with best dice tester.
Same goes for trade, it's bit irritating to transfer all stuff to one character every time I want to sell something to get best price with him/her.