Steve, I feel that because you think you know what happened you can't see the possibility of another scenario. What NaNu says makes sense. Nevill may well have rushed downstairs in order to pre-empt an increasingly aggitated Sheila from picking up the gun. She may possibly have been able to evade him at that point and run upstairs giving him time to call Jeremy, at which time it was only a question of "Sheila's gone mad and has a gun", not for a moment do I believe it crossed his mind that she would use it. I don't accept your constant assertion that they were barely on speaking terms but I do accept that they were very private people and everything possible was kept "in house." It is possible that up to that point no shots had been fired.
I agree with you, Alias and NN on this theory, April, I've never believed that Ralph or anyone else was injured at the time of the phone call to Jeremy, can only imagine why Ralph returned downstairs, why not use the phone in the office? Maybe he came down for a different reason, as the doors were bolted maybe to unlock the front door for Jeremy or who knows but someone got to him, poor man. Have only just thought about the fact the doors were locked and bolted, did Ralph expect Jeremy to climb through the window, or surely he would have unlocked the door for him, but maybe he didn't have an opportunity to do that.