Basically, this: https://forums.larian.com/ubbthreads.php?ubb=showflat&Number=880931
Allowing every companion present in party to chip in with a reaction instead of just one of the companions at random.
You are in a dialogue, the person you're talking to says something, then Gale comments on what the other person just said. Reload the scene - now it's Shadowheart that comments instead of Gale. The choice of "who chimes in" is random between the companions that have some thoughts on the conversation.
The mod "EveryoneInDialogue" does not accomplish this task, many confuse it as the solution but it only effects the dialogue option that show up on screen, not the companion interjections.
I pray to the God Modders of this community that this is even possible.