Let's assume KG was the target. The killer entered through the sliding door on 2nd floor. There would be no need to kill EC/XN. Go past that bedroom up the stairs to KG's room. Maybe both KG and MM were sharing the bed after staying up talking for a little. Kills both girls on third floor. Comes back down stairs but maybe either EC or XN heard something and got up to investigate. Let's say it was EC. Killer attacks and almost kills him. XN is still in bed, possibly still half asleep, calls out to EC and asks what's going on ... killer decides to kill her just in case she has seen him, which is why she has defensive wounds. Killer flees. EC badly wounded tries to crawl to where XN is in bedroom, but dies. Maybe his body can be seen from the front door and his friend who was meant to come in the morning spots him, goes inside the house, can see that EC is in a really bad way, there may be some blood, but not as much as where he was originally stabbed, and he is face down, so the friend can't tell how bad he is but knows he's not responding. Spots phone on the floor, grabs it and calls 911.