I have found Holly’s theory and it seems she has put her money on the first scenario I painted
“It seems clear to me that NB and SC were downstairs. NB phoned JB. Meanwhile SC goes upstairs and shoots June *5 or 6 times. NB races upstairs and as he approaches the bedroom door he is stood on the landing stairs putting SC in an elevated position at the bedroom door which accounts for the downward trajectories of NB's lip and jaw gsw's. NB then turns and is positioned on the main stairs facing down towards the hall when SC repositions herself either on the winder stairs or main stairs and fires down hitting the rear of NB's shoulder and elbow/chest which again accounts for the downward trajectories to the rear of his body.
Once NB and SC are in the kitchen poor NB is so badly injured he is unable to put up any sort of resistance and is beaten with the rifle and then sustains the four gsw's to the head.
June staggers around the bed clutching the bible but drops it pretty much where it was found. She manages to stagger back to the corner of the bed near the door where she sustains the two fatal gsw's to her head.
After the twins are shot SC enters the main bedroom via the box room and takes her own life. When she enters the main bedroom she inadvertently moves the bible with the door causing the mirror staining.
I think it was all over very quickly and more than likely before the police and JB arrived.”
So we have to accept that for reasons unknown both Nevill and Sheila found themselves downstairs at 3 in the morning, and that for reasons unknown and witnessed by Nevill Sheila picked up gun, attached magazine, did not turn it on Nevill at that point (would have been a good idea seeing as how he was her biggest threat) and instead turned her back on him (leaving him downstairs with the phone and other guns), went upstairs, Nevill picked up phone, Jeremy answered (was his phone next to his bed, if not how long before Nevill got through?) Nevill said the immortal words “Sheila’s gone crazy, she’s got a gun”, moments later heard gunshots but didn’t mention these to Jeremy, dropped phone and decided it was time to tackle Sheila. Meanwhile Jeremy hung up his phone, dialled Nevill back immediately but got an engaged tone despite the phone being off the hook, he rang a couple of times having a last number redial button on his phone which he says took 20 or 30 seconds, hung up again and was able to phone his girlfriend. 10 minutes later he gets through to the police.
No, I’m not buying that, it doesn’t sound plausible at all.