Well, since I think this is custody related, and I think it was provoked by JWs mother... Even if he got custody, the child would still be exposed to people in the R family...and I think she did not want the child in that environment. The only way to do that is to eliminate those closest to that child.
Eliminating not just HR but her parents and siblings would also eliminate the most likely people who could have posed any viable custody challenge. In that theory GR is just in the wrong place at the wrong time.
Of course that doesn't explain the death of KR unless he was simply killed because he saw something or heard something.