Doctor Who stars Jon Pertwee and William Hartnell appeared together in one film.
The House That Dripped Blood has Pertwee, plus three ‘unofficial’ Doctors: Peter Cushing, Geoffrey Bayldon and Joanna Lumley (uncredited)
Not often.
Michael Keaton x Val Kilmer: none listed in IMDB
Michael Keaton x George Clooney: Out of Sight (and Keaton’s appearance is uncredited)
Michael Keaton x Christian Bale: none
George Clooney x Val Kilmer: none
George Clooney x Christian Bale: none
Val Kilmer x Christian Bale: none
Adam West x all of the above: none
Robert De Niro played Al Capone in The Untouchables (1987) and F. Murray Abraham played Al Capone in Dillinger and Capone (1995) before they appeared together in The Bridge of San Luis Rey (2004).
They appeared in Man of Steel together. One was his birth father, the other was his adoptive father, and both actors had played Robin Hood, so this definitely counts.
Ben Affleck is about to be added to that list. Has he been in any movies with any of those actors?
This doesn’t really count, but it’s a neat little piece of trivia I’d like to pass along: Sam Waterston and Michael Moriarty, who both fulfilled the same role as ADA on Law & Order, although as two different characters, were in a production of *The Glass Menagerie *together, with Katharine Hepburn as Amanda, when they were much younger. It’s fascinating to see. It was a stage production, but there is a film of it done for television, IIRC, by WGBH-Boston, the PBS station.
Does this count?
Phyllis Frelich played Sarah Norman on Broadway in Children of a Lesser god; Marlee Matlin played the role on-screen; then, they both appeared together at least once that I can remember, in an episode of CSI.
Liv Tyler and Jennifer Connely played sisters in Inventing The Abbots. Later, Connelly played Betty Ross in Hulk and Tyler played Betty Ross in The Incredible Hulk.
Blofeld was memorably played by Donald Pleasence in You Only Live Twice, which also featured Charles Gray – who later played Blofeld in Diamonds Are Forever.
OK, this is a bit of a reach, but…
There was a commercial (I forget for what) where Charlie Sheen is waiting in line for something. The wait is so long, that he turns into Martin Sheen. So, technically, they played the same character in that commercial. They were in Wall Street and Cadence together.
Michael Caine and Sylvester Stallone co-starred in the soccer movie Victory.
Stallone later starred in a remake of Caine’s film noir Get Carter (Caine had a small role in that movie).
If you consider Dr. Gregory House as a variation on Sherlock Holmes, then Hugh Laurie (House) played Benedict Cumberbatch’s (Sherlock) father in the short-lived series Fortysomething.
Well, not exactly what you wanted, but…
Max von Sydow (Jesus) and Telly Savalas (Pontius Pilate) co-starred in ***The Greatest Story Ever Told.
Savalas played Blofeld in On Her Majesty’s Secret Service while Vob Sydow played Blofeld in ***Never Say Never Again.
Matt Damon, Barry Pepper, and John Malkovich have all played Tom Ripley in different films. Damon and Malkovich were in Rounders together, and Damon and Pepper were both in the True Grit remake.
Kevin Costner and Sean Connery co-starred in The Untouchables.
Costner played Robin Hood in Robin Hood: Prince of Thieves, while Connery played the aging Robin Hood in*** Robin and Marian.***
Burt Lancaster played the small but pivotal role of Dr. Archie “Moonlight” Graham in Kevin Costner’s Field of Dreams.
Lancaster played Wyatt Earp in Gunfight at the OK Corral, while Costnerp layed Earp in the unsuccessfull Western Wyatt Earp.
Paul “Fast Eddie” Newman and Jackie “Minnesota Fats” Gleason co-starred in The Hustler.
Decades later, Newman starred as con artist Henry Gondorff in the Oscar-winning hit The Sting. Jackie Gleason played Gondorff in the flop sequel The Sting II.
Robert Mitchum played hard-boiled detective Philip Marlowe in*** Farewell, My Lovely.***
Elliot Gould played Marlowe in The Long Goodbye.
Mitchum and Gould both appeared in the godawful kangaroo movie Mathilda.
Al Pacino and Robert De Niro both appeared in The Godfather: Part II.
Al Pacino played Satan in The Devil’s Advocate.
De Niro played Satan in Angel Heart.
The character of Satan might be as rich a vein as Wyatt Earp. 