NEW THEORY (mostly because I'm having withdrawal from the case now...)
What if....it came down to only 2 people and one dog? And JOK never did "make it in the house" which is why he wasn't seen.
The 2 Brians - BH & BA hanging on in the garage with Chloe - maybe one of them smokes in the garage while Chloe is let out the backyard. They don't want Chloe in the house because it's crowded.
They see JOK coming up the lawn, open the side service door to the garage and wave him in. Confrontation over KR turned into a scuffle which turned into Chloe jumping in and JOK falling and hitting his head. Music in house loud. Voices in house loud. Door to garage shut. Maybe music playing the garage? But whatever happens, happens quickly and fairly quietly and goes unnoticed. Because they are drunk and stupid, they panic. They know KR is outside and are freaking out. So they slip inside and act naturally and no one suspects a thing. Karen leaves. Everyone goes home. BH decides to go to CPD for an alibi because he knows he will be seen. Maybe he goes and does some other stuff, doesn't matter at this point.
Meanwhile, since JOK is now in a semi-warmish garage, a bit warmer than outside, the phone begins to cool at slower rate. NOTE: I do NOT believe Jen made the search at 2:37 am. Maybe she made the search in the morning. Maybe KR asked her and forgot. Who could blame anyone? It was chaos! BH calls BA - all good? Need anything? BA says no - go home. I've got this. Maybe he runs and gets Chris or reaches out another way and Chris comes help him move John to the curb to make it look like a snow plow hit him.
Someone (BH/BA) goes to 1 Meadows and finds the piece of tail light in the driveway that they had heard she cracked and takes it back to BA house and drops in the snow to be found that first evening by SERT team. Is that enough? Maybe not. BH decides to smash the tail light more and sprinkle the rest of the pieces throughout the yard to strengthen the case. Cops, judges, DAs, etc...usually have no problem believing one another rather than an outsider, so they move forward believing everything is just as it seems.
The rest can easily be explained by a combination of confirmation bias, family loyalty, blue line loyalty, or just truly not knowing or feeling intimidated to even state any of their suspicions particularly because they have no proof. Maybe the wives and some family have an idea, but it isn't necessary that they are in on the plot. Maybe they just turn a blind eye. Or maybe they literally do believe KR did it and are helping as much as possible.
It's not that hard to understand and there doesn't need to be 20-30 people colluding to cover up a crime.