Continuity mistake: The dog changes from a regular color collie to a dark almost black collie several times throughout the movie.
Other mistake: A shootout occurs in a hotel, where a shotgun blast apparently opens the money box. None of the perpetrators fired into the room.
Answer: According to Wikipedia, the shootout at the ranch, both Devries brothers are killed by Jeff McCandles, before being shot himself. The rest die at the end of the movie.
You only see the older brother shot by Jeffrey before being shot himself. I only assumed young Billy stayed behind to help his brother.