So you're saying that at this stage Sheila has shot Ralph(Nevill) once,he decides to try and conceal the fact that it's a family member so he contacts another member of the family,Jeremy on the telephone to keep the incident "in-house". But we have to explain why this telephone call is interrupted suddenly,and how Nevill manages to make a further call to the Police. If Sheila is standing over him with the gun at this stage and he puts the receiver down,then she gives him the severe beating with the rifle butt it would explain the blood in the telephone area but not where Nevill's body is eventually found.
However if it was Jeremy who came into the master bedroom after having shot the twins in theirs it's possible that Nevill is waiting for the intruder. Jeremy starts firing at Nevill and June,but runs out of ammunition and has to reload the gun. Nevill manages to get onto the landing and moves downstairs to attempt to use the telephone. Nevill is shot once more on the landing but manages to get into the kitchen as far as the kitchen worktop where he rests his bloodied hand,but by this time Jeremy is there and fires at him again. Nevill instinctively heads for the kitchen door where he is finally killed and bashed by Jeremy. In this scenario there is no telephone call. Then Jeremy goes back upstairs to finish off June,who by this stage has managed to drag herself to the door,where she dies with a gunshot between the eyes.
He then goes to Sheila,who as Pamela Boutflour said at 10pm the previous evening sounded like a zombie,and who would go to her death meekly not knowing anything about it.