The murders likely happened around 9:40pm-10pm. Right after Rose went from the park or bar. The killer followed her at some distance and stroke right when she was entering the room or minutes after with the killer knocking at the door saying he was the motel manager or room service. However in that situation, Roger would have dressed unless Rose was the one asnwering the door and he stayed in the bathroom. How could you think the murder happened at 11pm, midnight or even 1am? With Rose dressed? How come?
I'm not 100% sold on the car being moved as the point of entry. If it were the step-father and CRH, then that would be my guess, but if half-brother was involved, other possibilities open.
We know there were two calls to or from the babysitter (mother) and another unknown call.
Call one to babysitter seems pretty standard. "Hey, I just wanted you to know I'm at the ____ and my number is ______ if there's any emergencies."
Call two could've been a lot of things. It could have been something Rose just forgot to say, but I can also see call two being relevant to who was coming. "Hey, your brother is out that way and wants to talk to you. Is it okay if I tell him how to reach you?"
Maybe call three connected to all that further. And if she made a call from the bar, and if she was acting in a way that caused a confrontation, then it's possible she knew he was coming. Maybe she met him at the bar. Maybe outside. Maybe he said "I just want to meet this guy."
Maybe he was pissed off and a conversation escalated. He was probably not happy she was with a guy in a hotel out of town while mother is watching the kid (assuming babysitter is mom). She might have stood up to him with Roger's help. It's possible a conversation surfaced that hinted at, or addressed, sexual abuse. Maybe Roger even knew family drama when half-brother enters and confronts him about things he's done to Rose. It seems that all three in the room would have had secrets they wouldn't want exposed.
Then there's the idea that maybe Rose's daughter is also half-brother's. Not saying that's true, but if it is, he has some real investment in how that kid is raised. The fact that he cared for her after Rose died would prove that he must have made some kind of effort or earned some kind of right to that child.
If it was half-brother, I'm about 50/50 on the possibility of just being followed and wedging his way into the room. I think the phone calls matter. I think mother as a babysitter matters. I still think the bar encounter matters. I think there would have been a somewhat sizable conversation or confrontation. I would personally move the time of death back due to all of this.