How many actors and actresses have won Oscars for their performance in Sidney Lumet films?

Explanation

Sidney Lumet is considered one of the 'grand old men' of film history. He started off as a television director, but since gained tremendous success as a film director with the 1957 film '12 Angry Men', for which he also won an Oscar for best feature film. Other famous Lumet films are 'Network', 'Murder on the Orient Express' and not least 'Dog Day Afternoon', starring Al Pacino. Lumet's biggest force was his ability to direct his actors, which also means four actors have won Oscars for their performances in Sidney Lumet-films.