People all know that the Keach, Carradine and Quaid brothers appeared in the film, but I hardly ever hear mention that the actors who appeared as the Ford brothers were also brothers in real life, Christopher and Nicholas Guest.
I feel they were introduced far too early in the movie and it was anachronistic, but it did add to the movie.
I read an interview with David Carradine in which he claims that the brothers Bridges were supposed to play those parts but dropped out because Jeff didn't want to be the guy who shot Jesse James. I thought that was interesting, partly because I never gave much thought to just how many brother combinations would be possible.
http://www.avclub.com/content/feature/random_roles_david_carradine
Anachronistic? Yes. The movie is, obviously, not a history or documentary piece and it is wildly inaccurate but it is one of my favorite westerns.
They were named in the previews, listed in the credits, and had a big role at the end. What did you miss?
If we all liked the same movie, there'd only be one movie!