To make it look like it couldn't possibly be them. They staged the scenes, I believe, to make it look like something that it was not. If they just killed CR1, DR, HMR, and CR2, it would have pointed squarely at them. Kill the entire family, including the brother who also had a grow, and it looks more like drugs. They over-staged it though. Dewine basically said so on day one. The over-staging, showed they knew the family inside and out.
It was CR1, GR, and KR's deaths that told me that they knew these folks and knew them well. The dogs, CR1's dogs lounging in a recliner, on the porch, that morning. KR's dog, who reportedly, Stone had to restrain for LE to go inside that afternoon. The missing cameras, CR1's motion lights, getting around CR1's property, and the ability to get inside at least three of four properties without being heard (keys?), in trailers, no less.