What are the names of the three actors (resp. the characters) standing around the snooker table in A Clockwork Orange?
The man sitting at the table is Mr. Alexander (Patrick Magee).
According to this screenplay, "Rubinstein, Julian and Dolin also listening to Beethoven played loudly on tape recorder." Julian is his manservant (pink shirt), and Dolin (foreground) and Rubinstein are political cronies. Rubinstein is played by Margaret Tyzack, Julian by David Prowse, and Dolin by John Savident. A description of the scene is on page 165 of Stanley Kubrick: Seven Films Analyzed by Randy Rasmussen.