These are my thoughts on the murders., stated briefly, and subject to change at any time.
MM. I believe she was the primary, and possibly only target, initially, and the plan was to brutally kill her with a combat knife. Have believed this since very early on.
KG. She is the one of the four that I waver on, but I really believe she was killed because she happened to be in the bed with MM when BK went into her room. Whether BK even knew that she was at the house, or not, I have no idea. Had KG been asleep in her own room, I am undecided if she would have been killed. If he had stalked the girls or house to any extent, he may have known that the two were besties, so he may have killed her too., as an extention of his likely rage aimed at MM
XK and EC. Killed because BK heard and stumbled upon Xana as he was coming downstairs after leaving MM's room. (I think MM and KG were killed first). I think she may have been attacked, trying to run back into her room, but not mortally wounded, and then EC was killed, only because he was there, and could be a witness, before he returned to finish off XK. I think both of these murders were unplanned, but accomplished with no hesitation or remorse.
DM. Alive because I believe BK was in a hurry to get out of the house by the time that she opened her door and saw him, physically and emotionally spent after brutally killing four people, including at least one who reportedly put up a fight (XK), and may have feared that 911 had been called. Also, Murphy was loudly barking. Not even sure that BK actually noticed her as he was leaving.
BF. Downstairs, alone, where there is no evidence at all that the killer ever went.
All of this is JMO.