Could be, but not likely. Imagine you are there to carry out FIVE murders, do you really think you have time to stage manage the individual killings? Personally I don´t think so. The killings of the poor little boys was overkill - it was PERSONAL, not cold, calculated with the motive of getting rid of them for money.
There was not much stage managing was there ?
The twins & June were shot in bed. There was a big mess in the kitchen. Putting an open bible next to Sheila would not take long. Once everyone was dead Jeremy, if he was the killer would have had all the time he needed to do any stage managing.
If Jeremy could fire one shot into the twins, he could fire several shots. It would back up the 'shes a nutter' & 'gone crazy' quotes he gave the police later.