Quiz: Guess the last name!

Tags: 
  1. Janet, Vivien --> Leigh (by riffraff000)
  2. Howard, John -->Hughes (by riffraff000)
  3. John, Cynthia --> Nixon (by Rushmore), Lennon (by Imposter), still another possibility)
  4. Henry, Peter --> Fonda (by riffraff000)
  5. Tony, Jamie --> Curtis (by riffraff000)
  6. Hugh, Cary --> Grant (by riffraff000)
  7. Patrick, James --> Stewart (by riffraff000)
  8. Sofia, Francis --> Coppola (by riffraff000)
  9. Gene, Billy --> Wilder (by riffraff000)
  10. John, Glenn --> Close (by Rushmore)/ Ford (by Imposter)
  11. Danny, Walter --> Glover (by Rushmore), Crispin (by ash_campbell), Huston (by Cosgrove)
  12. Christopher, Spike --> Lee (by riffraff000)
  13. Michael, Roger --> Moore (by riffraff000)
  14. Tim, Woody --> Allen (by riffraff000)
  15. Robert, Fiona
  16. Dennis, Randy --> Quaid (by riffraff000)
  17. Eric, Julia --> Roberts (by riffraff000)
  18. Rory, Kieran --> Culkin (by riffraff000)
  19. Martin, Charlie --> Sheen (by riffraff000)
  20. Geraldine, Charles --> Chaplin (by riffraff000)
  21. Michael, Cameron --> Crowe (by Imposter), still another possibility
Author Comments: 

These people have got the same last name.
EXAMPLE:
Audrey, Katharine --> last name: Hepburn

Henry, Peter = Fonda
Tony, Jamie = Curtis
Hugh, Cary = Grant
Patrick, James = Stewart
Sofia, Francis = Coppola
Gene, Billy = Wilder
Christopher, Spike = Lee
Michael, Roger = Moore
Tim, Woody = Allen
Dennis, Randy = Quaid
Eric, Julia = Roberts
Martin, Charlie = Sheen
Howard, John = Hughes
Janet, Vivein = Leigh
Rory, Kieran = Culkin

Geraldin, Charles = Chaplin ??

Excellent!

ok well: (great idea by the way)

John + Glenn = Close
Danny + Walter = Glover
John + Cnythia = Nixon

I'm glad you like this.
Your three answers are correct, even though these are not at all those I was thinking about.
Those I expected, are by far more obvious (than John Close, Walter Glover and John Nixon).
Hint: Glenn --> man!!!/ Danny is Walter's grand-son and Cynthia is John's daughter!

John, Cynthia - the only other name I can think of right now is Lennon, though those two are ex-spouses
John, Glenn - Ford
Michael, Cameron - Crowe

John and Glenn Ford are definetly those I was thinking about, too.
John and Cynthia: Another hint: they were both in one and the same movie.
Michael and Cameron: Correct, but there is yet another possibility, by far easier. Hint: They are both from a big family of actors.

11. Crispin (watch out for those karate kicks, Letterman!).

OK, but there is still another solution for #11! It is so obvious!

Jeez, people... #11 is Huston!

Uff...finally! Thanks Cosgrove!