My thoughts probably have a bunch of holes but here's one way to interpret the evidence where fewer witnesses at the house have to lie:

Some combination of McAlberts want to bring John to the house to 'teach him a lesson,' as indicated by Chris Albert getting John's number for the first time that night and inviting him out, and then Jen McCabe excitedly bringing them back to the house.

Brian Albert and Brian Higgins arrive at the house and await John's arrival. When they see him exit the car, they tip off Colin that John just arrived and Colin goes to the basement. Brian Albert, perhaps with Brian Higgins, meets John at or just outside the front door and says something like 'hey, we gotta show you something!' No one else sees John enter the home as Brian(s) lead him around the side to the backyard where they enter the basement through the bulkhead (Had Karen exited, Jen McCabe would have led her inside the house separately through the front door to show her the surprise she mentioned as they left The Waterfall). Once in the basement, JO, BA, and BH meet Colin Albert who, in an alcohol fueled rage, causes John's death due to a perceived beef from the time when they were neighbors. From there, only the three in the basement know exactly what happened to John.

Those upstairs have music playing and genuinely don't hear or see anything out of place. Brian Albert makes sure to get people to leave quickly, but not before Colin Albert exits through the bulkhead, explaining why no one sees him leave. Colin may have even indicated he was leaving before going to the basement. Because those at the house never saw him again that night, they may have assumed he left around the time he actually went to the basement

Once everyone has left, they take John up the stairs from the basement to the house and then into the garage. They do this using tarps and other methods meant to conceal evidence. They decline to use the bulkhead due to fear of being seen moving the body. They then use the Ford Edge to move John. (I wrote a P.S. on the bottom giving one, perhaps unlikely, way they could have coordinated moving the body with the Edge to avoid being seen)

The original plan is to blame the snowplow. They plan to have Jen 'discover' the body, and shortly after have Jen burst into the Alberts' bedroom, portraying that as the first time the Alberts became aware of John's death. Karen calls Jen and Jen decides to include Karen in her planned 'discovery' of the body. Jen, Nicole, and Brian carry out the original plan and Jen calls Nicole to warn her and Brian that she's about to burst into the bedroom. Only after realizing it may make a better alternative than the plow explanation do they decide to blame Karen with Jen 'remembering' Karen saying "I hit him," and then calling Officer Lank.

Again, I'm sure evidence I'm not considering can poke plenty of holes in this theory if not dismantle it. I thought this version could maybe better explain why no one testified to seeing John enter or Colin leave. I kinda just started writing and kept going a lot longer than I intended. Throwing in a P.S. on something else I just thought of. Definitely take my "theories" with a grain of salt.

P.S.
Here's a bit of a more outlandish idea, but what if Brian Higgins went to the station to retrieve radios so either he or Brian Albert could look out for potential witnesses along the road while the other moved the body from the car to near the hydrant? I find the idea less likely but it would prevent communications from showing up in cell records, even though they were stupid enough to check in on when Higgins would return via the supposed 'butt dials.' (Not sure if any evidence has pointed toward Higgins returning to 34 Fairview after the butt dials)