I suggest add a timer, let's say default 5 secs, but could be a config param, before a conversation starts, when playing in multiplayer.
Allowing for other players to join in at the same time as the first speaking. Maybe a pop-up about the players portrait which is initiating a conversation, where you can press join and will join in automatically.
There is a lot of other posts about being able to take over a conversation or changing characters during a conversation. That'd all be good.
