Revealing mistake: Early in the movie when the maid is opening the drapes to let in the morning sun, the sun lights the room a half a second before the drapes are actually opened.
Revealing mistake: When "Dog" is chewing on one of the men on horseback's arms, after he lets go, the blood on the guy's arm couldn't look any more phoney.
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.