My Contact tells me that Rose said Peter CALLED her and told her the girls were dead. We don't know if the call was before or after the 911 call, but when Rose arrived at the scene, she already knew the girls were dead. Peter wouldn't have called her on the phone if she was standing right there...he called her before she left the farm or while she was on her way to the Placker house. Peter went to meet Rose at the car to keep her away from the crime scene, Rose already knew Skyla and Taylor were dead. You quoted the exact information about the call to Rose from Peter in your post: Rose said that when Peter Placker called her to tell her he'd found the girls dead he said "when we got home they weren't here and I went looking for them".
BTW, Rose already knew something was wrong when Skyla didn't answer her phone (the 2nd call Rose made) - that's why she called the Plackers just after 5PM, because Skyla wasn't answering her phone. Then Peter (or Vicky) tried calling Taylor on HER phone - no answer. At THAT time (5:10 or so), the Plackers were NOT AT HOME, so as soon as they did arrive home (around 5:20), Peter walked down the road to try and find the girls. He knew neither girl was answering her phone. Maybe he could even hear one or both of the girl's phones ringing as he walked toward the crime scene - I can see where Rose would just keep dialing Skyla's phone (and Vicky might have kept dialing Taylor's)
All we don't know is if Peter called Rose before or after the 911 call? It would be on the phone records for whichever phone he picked up at the scene to call 911 (obviously he did not bring his phone with him). Or maybe Peter called Rose on Skyla's phone and 911 with Taylors? It seems to me that Peter knew Rose was coming (so he had to stop her down the road) - how would he know that unless he talked to her and told her the girls were dead and told Rose where they were? Rose was just a short distance N of the crime scene, it would have taken her maybe 5 minutes to get there - I think she was waiting to hear from Peter or Vicky that the girls were back home BEFORE she got in the car to come get Skyla.
And I think this is what might have happened...Rose couldn't get ahold of Skyla, she called the Plackers and they said the girls went for a walk, and they would call Taylor's phone (like maybe Skyla left hers at home or something). Rose gets worried, maybe Claudia Farrow says "I'll walk up the road - maybe I'll see them walking over here" (because Skyla knew her mom was at the Farm/Ranch where Claudia and Jimmy worked), meantime Peter can't raise Taylor on her phone so the minute he arrives home he runs immediately up the road calling the girl's names. He doesn't bring his phone, maybe because Vicky is using it to call Taylor? Peter finds the girls and then calls Rose and tells her to come, the girls are dead - maybe calling Rose (and maybe Vicky too) BEFORE he dials 911 (it's obvious the girls are dead, there isn't any immediate rush to call for help and that call might explain the few minute's delay in calling 911). Rose calls her Mother Who is out looking for the girls) and tells her - and either Rose picks up Claudia and she arrives with Rose or Claudia gets the call and goes back to the Ranch, gets her car and follows a few minutes behind Rose. Vicky also runs to the scene. Peter is on the phone with 911 and is keeping everyone away from the bodies until LE arrives.
Maybe that's how it went down???
My Opinion