That sounds like a very good suggestion OP. Didn’t try in Coop, but I would find it detrimental if followers of each players wouldn’t be recognised, if they are not the ones leading the conversation.
Overall, I think BG3/D:OS2 would, benefit from a more “party based” dialogue system. Considering how little identity as a leader there is to our main in singleplayer, and how much the game supports coop, I think making the dialogue system more of a party interacting, rather then single character interaction would make more sense.