I just watched Luke Rhoden's testimony, which I think opens up a clear hypothesis. It's always bothered me why they went around and killed Kenneth. It's not like he would get custody of Hanna's older girl.
Remember 2 points in Luke's testimony:
1. Billy saying to Luke when they (CR, KR and Luke) came over to warm up the backhoe so BW could start it that CR and KR were good people but if he got into a beef/a fight with them "he'd half to kill them." I take that to mean that if you go after a Rhoden, you were in for the fight of your life. BW took these men seriously.
2. There was just a brief question about someone beating up/fighting with CR and Kenneth going after that person to retaliate.
The prosecution has to be going somewhere with these points.
If we assume that custody is the prime motivator, it would never be enough to kill just Hanna because it would point right to Jake and the Rhodens would go for custody. (Jake still had that little sex with an underage girl problem.) So killing the folks on Union HIll Road was necessary to cover the motive and to eliminate competition for custody. (although I still don't get why Frankie and Hannah Hazel had to die and you could imagine a sane person not killing CR or GR).
However. It's obvious from the above that BW knew Chris and Kenny would go after whoever killed Hanna, Dana and Chris Jr. So eliminating Chris was essential to the plan. But BW also knew that if Kenny figured out who did the killing, then KR would be coming for him. In essence, BW knew the Rhodens well enough that he feared retaliation so he wiped out those likely to retaliate. In my view, that's why KR had to be killed. BW feared him. I also think BW might have had other motives not necessarily evident to his sons, in terms of personal rivalry over the drugs or something else we haven't heard about yet. Not even my opinion--just thoughts from what I've heard and seen today.