I dont think the bedroom soc is compatible with JB entering through the main bedroom door and shooting June and NB in that room. If I consider the guilty scenario of JB (considered a marksman) entering the main bedroom via the landing and first shooting June in Bed with NB fleeing his bed before any shots were fired, how did NB end up in the doorway as per the bullet location? Imo the innocent scenario of SC and NB in the kitchen, with NB distracted by making a call to JB, and SC moving upstairs to shoot June from the foot of the bed with NB dropping the phone, running upstairs and arriving at the entrance of the main bedroom appears more compatible with the soc/bullet location?
I'm unable to make out the wording in the shaded area. Think it might say position of shooter? If it does this would surely seem about right given the angle of shots /wounds and bullet location? I'm unable to work out how NB could flee his bed and get past JB without receiving any shots on NB's side of the bedroom.
I know there's N,E,S,W somewhere, but if I consider the head of the bed is N with June's side/main entrance is E, NB's side is W and the foot of the bed is S. The bullets were all found N/NE (excl SC's). It makes no sense to me how NB could move from W to S to E to NE and only receive shots in the NE zone.
The Anschutz ejects used shells from the right hand side exit hole, so the obvious place where shooter fired from is the hatched area where most of the shells ended up on the carpet, which is what it more or less says on the diagram. I worked out exactly what it did read once, but don't remember the exact wording.
I can't understand why you don't see how simple the answer is. The attacker's intention was to kill everybody with head shots while they were asleep (it worked successfully with the twins). Nevill was too sharp - his mouth wounds might have been received while in bed, although there is no evidence of blood on his pillow or bedclothes on his side of the bed. Maybe he got up too quickly for any to have dripped there, and only started to bleed profusely once he had got out of bed. Or he was shot while standing at his side of the bed, possibly near the end and facing towards the main doorway.
A plan specially made for you...

Nevill didn't necessarily receive any shots in the NE zone... June was wandering about occupying that area after being shot anyway.
The killer is thought to have stood in the hatched area and fired from there roughly westwards towards Nevill on his side of the bed. If Nevill was desperate to escape his attacker then he probably pushed his way past JB to get away from the onslaught. He might even have received the defence wounds to his forearm in the bedroom (rather than in the kitchen) before shoving his opponent out of the way. There was a bullet casing found on the stairs which probably accounted for the arm wound Nevill received on his way downstairs.
According to your theory, if Nevill came into the bedroom from the landing, then in order to receive the wounds to his mouth he must have moved fully into the room in the region of his own bedside and turned round to face his attacker. But the more likely scenario is that as soon as Nevill realised that Sheila had hold of a weapon, he would attempt was to disarm her, rather than waste time phoning his son or the police.