My thinking for quite some time is that Kaylee started in her own room and was alerted to the intruder by Murphy. As Dylan indicates, it was likely Kaylee's voice that said, "There's someone here." Whether this initiated in her own room or Maddie's, they both died "in" or "on" Maddie's bed. (I think "in/on the bed" is more about semantics than location, but it's arguable.) IMO the order in which victims are listed on the PCA (MM, KG, EC, XK) is the order in which they died, and Kaylee's tearing/slashing wounds from lungs to liver follow with her being in a standing or sitting position rather than being prone like Maddie who was first. I still see Kaylee following Murphy into Maddie's room and running straight into BCK, but she might have been sleeping there (a tight fit when she could've laid on the bed across the hallway.) This encounter between BCK and these first victims is what generated the noise Dylan mistook for Kaylee playing with Murphy; however, I don't think Murphy started the relentless barking until he heard the noise from Ethan and Xana being killed right below when he was locked in Kaylee's room directly above them. As Steve Goncalves said, "It was a hell of a battle going on down there from what the coroner told us." This is a slight reconsideration of my first timeline regarding when/why Murphy started barking.
Idaho murders: Father of slain victim says she had 'big open wounds,' calls police 'cowards'