Came here via six degrees of separation from this story. Was hoping for a non-Austin related story, but looks like I won't get my wish. Been a rough few weeks in crime here. A few notes.
In Texas, as an example - any "unattended death" requires an autopsy. Meaning no one was in the room when the person died, and they weren't being "attended" to by a doctor, in a hospital setting, for example. A family member's death was considered unattended because the other family member was on the other side of the house when this person died.
If they were in the same bed when she died, and whatever state they were in has a similar law, it may have been considered not a case for a mandatory autopsy. Then again, the law can be applied inconsistently here in TX, as Antonin Scalia's death was technically unattended, but they did not require an autopsy. That can be a moving target, IMHO, no matter the state and circumstances.
Definitely doesn't mean a ball wasn't dropped, but another factor in whether an autopsy can be done (decided by the Justice of the Peace here, typically) is a religious objection.
I read this whole thread hoping for news of a forensic trail from the phones of the children. I hope there is one.