I may have figured it out but i havent fully fleshed it out yet.
From your event that casts to the controller in the character blueprint, drag a get all actors of class for the controller and run it in a for each loop. The exec is a branch with the condition being an equal for objects. The first object is the array element and for the second object, get a reference to self, drag from it a getaicontroller and plug it into the second object. If its true, cast to the controller with the object node being the array element. That way it should go through all controller instances and only cast to the instance that is controlling the character. And then do what you intend to do with the controller.
I’ve been way to demotivized to touch ue4 lately so if you can see if it works that would be wonderful.
Also if you can, tell me if it impacts the performance. A for each loop with alot of elemwnts and then a cast seem expensive to me, but i hope it doesnt slow down the game too much.