This is the second time John Lithgow plays more than one character in a movie. In Raising Cain (1992) he played multiple characters while in this one he plays twins.
Based on a true story.
On an article about the film, Bob Bradley said that John Lithgow would be his choice (and also Thomas choice) for their role if a movie about their life story would get released, after seeing the actor on a play many years ago. Sadly, Thomas didn't get the chance to see this film since he passed away in 1990.