I feel as you do, that it was a lot for just one person to be a target. I try to look at it as the killer would have been nervous to some degree, rushed, and possibly sweating at some point and when adrenalin takes over sometimes your mindset is super focused on an objective. I would assume not getting caught would be at the top of that list of objectives. We do not know who was first but I do know It takes a certain amount of fortitude and strength to kill in the manner in which the victims were injured. Let's say the last one put up a fairly good fight and it was just too much physically to finish the whole house. But additionally, you can think if there was a target K or M, they were not expected to be in the bed together so that may explain both being targeted. They have to go back downstairs, perhaps E and X woke up, one put up a fight the other a witness so both became the next targets, leaving no witnesses, and silencing them from alerting the police allowing them time to get away. I can not imagine killing all 4 unless the original plan of killing 1 went afoul and the rest were collateral damage or they wanted everyone and did not have the fortitude to complete the task. E was the most unexpecting individual staying the night. Anyone who knew of, or observed this home believed it to be a house of all girls.