Limiting entities a tamed mob can attack

I've been working with tamed entities recently, and I was trying to make it so that they wouldn't hurt other entities that the player has tamed. The problem is that conditions for when a mob will attack what its owner attacked seem to only be able to grab info about itself. No matter what I use, (source entity, immediate source entity, entity iterator [even though that one wouldn't make sense]), only event/target entity works and they will still attack other tamed mobs.

Is there any way I can make a tamed mob not attack certain entities or, at least, entities that the player has tamed?