truth vs. fiction
The movie, like the book on which it's based, takes quite a few liberties with the true story of the Maclean brothers (including the fact that they also had five sisters as well as the real circumstances surrounding Paul's murder, which actually took place in Chicago).
Here's an artiole from a Montana newspaper that separates fact from fiction and also contains reminiscences from some of those who knew both brothers:
http://www.helenair.com/articles/2000/07/09/stories/helena/c1a.txt