I felt the sister was being genuine and honestly believes everything she was saying.
The mother on the other hand felt somewhat disconnected and didn't show much if any emotion throughout the entire thing. I wouldn't be surprised if she had some knowledge of what really happened, but had she done it, I'm not sure she would have been able to keep it together to see her son "back from the dead" and act as if nothing happened.
Wish there was more on her brother (or was it his brother?) as it sounded like he could have been a suspect. But with the disconnection between the mother and the type of person her brother was made out to be, it's easy to form a story of them working together to get rid of the kid.
Though the way they described the boy, he sounded like one of the kids you just want to smack for being a stubborn turd. And they did mention him trying to run away before, so that possibility is there especially if he was pissed that nobody would come and pick him up that day.
Really, it was the sister who felt like she had some sort of emotional attachment to her brother. Everyone else just felt like they were telling a story of someone they knew but had no real investment in. Kind of jarring that people would be so detached to someone so close to them.