After going through the book a second time, I think the Carlyles are much more involved than what I previously imagined.
My theory is this:
Green spawns Rant, expecting him to go back to kill his mother and solidify their immortality. Rant rebels and attempts to protect his mother from rape.
Echo, Neddy, and Shot go back in time to save Rant's mother, Irene, from murder. This is the "sequence" at the beginning and the end of the book.
In response to Rant rebelling, Green spawns Bodie Carlyle with Mrs. Carlyle (this is why Rant inherently knows the smell of Bodie's mother). Green sends Bodie, once again, to kill Irene Casey. This may be what is insinuated at the end of the book, when Bodie, hiding in the darkness, enters Irene's house.
Originally, this may have been prevented by Echo, Neddy, and Shot. In response to this, Green goes back in time again and spawns Sheriff Bacon Carlyle, who arrests the gang before they can save Irene Casey (this is also why Echo states that Shot asking if Rant's mother had been murdered yet is the worst question they could have asked -- not because he was a sheriff, but because he was explicitly involved in the plot to murder Irene Casey).
Just a thought.
Also: Note that Bodie Carlyle, Bacon Carlyle, and Buster Casey all have the same initials.