The coroner also said some, but not all the victims were murdered in their beds. I know that could be taken very literal in that E (and maybe not K) were in their own personal beds (because they didn't live there anymore), but I think it's just as likely this means not all the victims were in any bed.
My own take on the coroner's statement about everyone being asleep is that the house was quiet, everyone was in bed for the night, not up and about, and that when the attacks started, everyone was sleeping. However, I don't think the coroner's statement necessarily means some of the victims didn't wake up, get out of bed, and perhaps try to defend themselves at the moment they were attacked. I'd be willing to bet that the first victim was killed in bed, though.
Interesting hypothesis, but I feel that if any of them were awake enough to get up and defend themselves against a single perpetrator that one or more would have escaped or had time to call someone. Likewise, I imagine the girls under them would have heard some screams or similar.
My opinion.