I agree with you guys and i have to add something on that case.
Since the game let you talk to somone multiple times (as many characters you have in party) then 3 options an be made.
1. All dialogues start with main character if he is alive otherwise ask to whom he will talk to. Once the dialogue is finished then thats it. You cant talk again with a different character and do different things. Also your main character receives the bonus persuasion of the highest among the party.
2. Always talk to the character with the highest persuasion values and if there are more than one having the same high values then ask to whom to talk to.
3. Every dialogue starts with a character picking phase so you can choose who will do the coversation