RobotStudio event

ESTOP between 2 robots and 3 push buttons

I am trying to add 2 controllers and 3 push buttons in a daisy chain configuration. Is this configuration not possible without a safety relay? No matter what I did with X1 and X2, I either get Controller 1 and 3 pushbuttons or Controller 2 and 3 pushbuttons.

Both are IRC5 Single cabinets. 1 running 6.12 and the other 5.15.