Susan,there was no blood drips,etc,leading from the bedroom downstairs to the kitchen that indicated that Neville had been upstairs.
Alias is right in saying that no blood was on Neville's side of the bed------------meaning that he wasn't shot upstairs because he hadn't been there. He may have attempted to have gone upstairs and was bashed for doing so,and so retreated back to the kitchen.
Had Jeremy done it,then he'd have timed it that they'd ALL been in bed,including his father,as Jeremy was no fighter and couldn't/wouldn't have attempted to have fought with his father,or he'd surely have come off worse,man to man. It was because Sheila was a woman,albeit an insane one,the reason that Neville didn't put up a fight.