Adam,,why didn't Jeremy kill Sheila first knowing that she was a " nutter " and capable of doing anything,,even picking up one of the guns and shooting him.?
Afterall,,Jeremy had experienced Sheilas' psychosis in the past.
Instead,,Sheila was the last one to die,,so how do you think that came about ? You'd have thought she'd have rang the police from the upstairs office while Jeremy was downstairs bashing his father ?
Sheila had,,afterall,,her children to consider,didn't she ? So in the time it took while Jeremy was down 3 flights of stairs,,,you can't tell me that Sheila couldn't have dialled 999 and WHF,,that's all it would have taken to have got the police out.