My thoughts are similar to yours but with one slight difference. I still think K was the target, based on intuition, her dad’s comments, and a few other things that are just my own opinion. I think BK went there to either kill K or both K and M.
I also think he killed M first, especially based on the sheath. Then I think he spent the most time on who he thought would be his final victim (K). Then X either was unfortunately in the living room/kitchen area when BK came down the stairs, or she heard K and M make noises and came out of her room. She was then killed. E was likely killed last in X’s bed/room.
Edited to add: this is also the order that the charges are listed in. First was the burglary (which obviously happened first), then M, K, X, and E.