As for broken couplers, you only need one of the couplings connected between two cars to work to separate the cars.
I have many cars that have one or two non working couplers as well as several with a broken couplers wired shut.
With many in those conditions, I am happy to have one working coupler per car. That is except for the rear of a diesel or a coal tender. My "To Do List" is too long already.
Charlie