When the door is activated, just check which collision box is overlapping the player
like [Collision Box]->[GetOverlappingActors]->Contains (GetPlayerCharacter)
Provided the collision boxes are components of the door actor. If not, you can actually do that without collision boxes: just add a Vector parameter to your interface call, and then you can calculate if the player is in front of the door or not, and drive your animation based on that.