The sheath next to Madison on her bed suggests that Madison was killed first. He pulled off the sheath, put it down, started stabbing, perhaps heard something downstairs (Xana was awake and safe at 4:12, dog barked at 4:17) ... why did he forget to pick it up?
Xana was not on tiktok at 4:15 a.m. Maybe she heard something at 4:12 and got out of bed to investigate when someone was at the bedroom door. She had defensive wounds and was on the floor, visible from the door. Maybe her body was the thud at 4:17, the dog started barking, D.M. woke up, Kaylee said "someone's here", then the murders of Madison and Kaylee, D.M.'s description of bushy eyebrows - was that a side view or front view? Side view means Madison could have been first, front view means Xana was killed first.
What does the timeline tell us? Why did Xana end tiktok at 4:12, but the dog didn't start barking until 5 minutes later? What was the thud, and was it the same sound that woke up D.M. or was there a second sound of playing with the dog? She knows who was killed first.