Use an event bus to notify the second controller of changes that happened in the first controller and vice versa.
Or even better, load the data onto the eventbus and both controllers can subscribe to that specific message and both will be updated.
When data change, throw the changes on an eventbus on the client side (something you'll need to build and event objects you'll need to define yourself). Both controllers will now subscribe to the eventbus listening for that specific event and if received, both will update their views with the data from the eventbus.