I concur. I think you and Tortoise have the gist of it. I'd still not discount mom, though. Was it substantiated that the boys heard mom tell EK to dispose of the body?
I'd say it's substantiated. Just to put it all together -
AW or HC said on NG podcast that they heard grandpa on loudspeaker recounting what he had been told. Grandpa had been told by whomever that 'they' didn't know which out of the two adults hit Mariah, if Mariah was dead and that KW said to EK 'get rid of her'.
It's somebody who was in the home to know this, who did not see it but heard it.
If it was KW or EK who said this to KW's father (or step-father), that would be an admission of conspiring to commit murder, given they didn't know if she was dead. If it was KW or EK who said this, grandpa would know which one of them hit Mariah.
It must have been one of the boys who said it and they were at that time living in the home of their grandma.
The only uncertainty for some posters is whether the minor made it up.
For the minor to not see but hear my guess is they heard KW and EK in an argument over getting rid of her, and it's likely an assumption that Mariah was hit. The autopsy could clear this detail up if say Mariah was strangled. The only way the minor would know Mariah was hit from another room would be if one of the adults said 'you hit her!' and the minor would have been able to say who did it, not leave it at either/or.
I am of the opinion that the adults discussed what they would tell LE before they called 911, purposely to create a version that the boys would hear and run with. KW telling EK to get rid of her would become KW telling EK to deal with Mariah crying. The boys then still trying to piece all this together but not willing to let go of what they heard now think Mariah was crying and they have an explanation for Mariah being hurt severely enough for the adults to get rid of her.
I contend that if the minor is fabricating all this, it's a pretty sophisticated lie that could see both mom and EK jailed for the murder of his sister, in a situation where the minor reportedly does not seem to be aware of his own love for his father, leaving him effectively with neither parent. Why would the minor not go along with the abduction story the adults put together? Why would the minor also implicate his mom and not solely EK if he is lying?
If the abduction was an alibi created to cover for the minor, even if he thinks LE is not buying the abduction story, he has adults who are covering his back, so why would he turn the tables on them? Would he think ahead that one of them might not stick with the cover story and get his defence in early? I don't think a minor of this young age, despite knowing that children are more than capable of lying, would be so prepared at that early stage of the investigation to not only have an alternative story close to the truth but not the actual truth ready, but also to implicate his mom as well as EK. If it was just EK, then possibly.
I believe what he said.