This is similar to another thread I posted in a few minutes ago, I really think Wasteland 2 nailed the dialogue system. For those who don't know/can't remember, any party member could talk at anytime and if they had any charisma skills (i.e. smart ass, kick ass) those specific characters could use them whenever the game prompted a use for them. A skill, like barter, is a 'dump' stat that is shared across the party, so no matter who is talking, the bonus(es) from the barter skill will be used. Imo, this is the correct way to do party dialogue in an RPG. This solves the problems of x is closer to y therefore only x can talk, "missing out" on dialogue because the correct character isn't being spoken to, and not being able to roleplay in general in the sense of pen and paper freedom.
However, topic at hand, I'm content with only the player themself can control their own dialogue choices, whilst the other NPC party members have their own AI. Having said this, though, this would not work if you had the ability to make 4 custom party members (which I REALLY HOPE is a thing for the main game).