I think part of the reason that CR1 was shot so many times is that they either woke him up, or he knew them and invited them in and it took that many to stop a moving target.
It looks more like to me that is different shooters. One, who is more adept/comfortable with, firearms, and/or killing than the other. I remember them saying that FG was shot through the eye too.
You have one seemingly more controlled shooter who possibly does the job w/
Three shots, one shot, and two shots, and probably helped take out CR1. Then the accomplice who helped with CR1, and shot Dana, HG, and probably HR. I wonder if one of the assailants was female?