These two performers made themselves well-known in this intimate Broadway musical revue, and almost simultaneously played in the film version of a landmark Broadway musical.
Who are they? What was the musical revue? What was the musical film?
Are you looking for Marge and Gower Champion? They starred in the 1951 movie version of Show Boat and the 1955 musical revue, Three for Tonight. Not quite simultaneous, but it's the closest I can think of...