though I don't know inner workings of the system enough to speculate in detail.
Me neither ...
But since it was allready done in other games (so often mentioned SWtOR for example, but i heared DoS2 had something simmilar aswell but dunno didnt play) i know it is possible ...
Oh it's possible alright, just the engine might not support something like that.
D:OS2 had nothing resembling that - it worked very much like BG3 now - one person would engage in conversation, and you needed to leave a conversation to restart it with another character. The conversation would start from the beginning with without acknowledgment that it was done before.