I'm not a Dev but BG3 does not currently have companion or summoned creature AI. Party members will only do what you tell them to do except for certain cutscenes. I have heard no indication from Larian that they plan to implement such AI.
Honestly I think combat would become too boring if companions acted on their own. You'd spend the vast majority of it waiting for enemies and allies to take their turns. Companion AI works best when turns happen simultaneously, something that is almost certainly not going to be implemented for BG3.
