How many movies have Willy Kaiser-Heyl and Willy Zeyn Sr. collaborated on?

They have worked on 2 movies together! Their first movie together was Der Hund von Baskerville - 6. Teil: Das Haus ohne Fenster (1920) and was their highest rated movie together. They have not worked together since Aus eigener Kraft - Ein Filmspiel vom Auto (1924).