How could Jeremy in his wildest dreams expect to be able to enter the farmhouse (with two - possibly - barking dogs) in the middle of the night and expect to control FIVE people? He could not know whether the twins would wake up - or if they WERE awake already. He could not know whether June, Neville and Sheila were asleep or not. He could not expect them all to be lying in their beds. He just couldn´t.
All the possibilities of it all going terribly wrong for him due to the fact that there were FIVE people to control, simply makes me believe that this crime was IMPOSSIBLE for Jeremy to have committed.
As I always say: if he had an accomplice, OK, I can see it happening, alone, NO!
And finally my favourite question for nons: where was Sheila while Jeremy was killing Nicholas, Daniel, June and Neville? Where - and what was SHE doing?