Possible Clues:

• Last name of both "The Ballad of Buster Scruggs" filmmakers
• Name on “Fargo” posters
• Either director of 2010's "True Grit"
• Either director of "Fargo"
• "Barton Fink" director Joel
• Either director of "The Big Lebowski"
• Either brother who co-wrote 'O Brother, Where Art Thou?'
• Director brothers' surname
• Name in the 'Inside Llewyn Davis' credits
• Directing family surname