Mike, that makes very little sense.
The officers who thought they say a woman later said it turned out to be Nevill.
Had Sheila gone upstairs, then it would come as a very big surprise that she'd head to her parents room, rather than her own, or the boys. Then collased on Nevill's side of the bed. She could have collapsed at any point downstairs, or on the stairs, but managed to make it all the way to the bed of the man she'd just killed and collapsed there...
On top of that, the police want to cover this up! - why? there still is no motive to do so, and the operation is far from botched. There would have been nothing wrong with a scenario where Sheila HAD been seen, presumed dead (but wasn't), then moved herself upstairs to commit suicide.
Why then stage manage anything?
Also, you are then having to involve other people in the supposed 'setting of the scene' - so multiple officers involved and SOCO?
It simply beggars belief.
A disturbed body in the heat of the moment - I can believe in.
A bent copper telling the story his way - I can believe in.
A familiar close knit team of coppers conspiring - I can believe in.
But the evidence just doesn't stack up. The confused logs stating '1 dead male, i dead female' are exactly that - confused logs. The logs also state ALL lights on' (they weren't) and two dogs barking (only one inside the house).
If they've falsified logs too, then why not rectify these issues too?
For me personally, I think JB did it. There is possibly a chance Sheila did it, but the evidence is weak (imo).
The only real mistake the police made was being too quick to presume murder+suicide, and potentially lost a lot of evidence as a result.