Complex sentence: Eddie gets word that his brothers have been marked for murder, and tries to warn them, yet what Eddie does not know, at least until the last moments of the film, is that Kubick is the man who has ordered the Rico boys murdered.
Split into simpler sentences: Eddie gets word that his brothers have been marked for murder. He tries to warn them, yet what Eddie does not know, at least until the last moments of the film, is that Kubick is the man who has ordered the Rico boys murdered.