It strikes me that all this JB cunningly tried to frame his sister just doesn't add up at all. He's somehow predicted that in years to come, it would become widely known that there are numerous incidences of mothers killing their own children, due to a combination of mental health issues and fear of losing their children. Back in the mid 80's? No. Not widely known at all. To coin a phrase oft used by certain posters, A far simpler explanation would be for Sheila to be one of the first of an increasing batch of mothers who would go on to commit these tragic crimes in the modern era.
Portrayed her as a 'nutter'. The term 'nutter' was an extremely common phrase used back in the 80's, at a time when people in gerneral displayed less respect, empathy and understanding towards people suffering mental health issues. It was a Thatcherite 'sink or swim' mentality. JB portrayed his sister in much the same way as she was portrayed in her last known telephone call to another prosecution witness, i.e. listless, distant etc.
For somebody who has supposed to have set Sheila up, just when things were going to plan, instead of exclaiming woe about how his nutter sister has just killed everyone I told you so etc, he blames 'those men with the guns' who went in to the farmhouse.
The setting up of Sheila is fantasy.