Regarding the alleged phone call from Ralph to JB.Could be that it simply was all part of JBs plan to frame Sheila.Or it is possible that Ralph was made to make that call.In that scenario its possible that somebody wanted JB at the farm in order to be killed aswell,or somebody wanted him at the farm to be caught there by the police and deemed as a suspect.The more I dig deeper into this family,the more I realise that anything - in fact - is possible.
But probably not this scenario.
The killer stumbled upon a loaded gun left by JB, they would have had their own,if nothing to do with JB.
Big risk getting Neville to use the words that he used, in the phone call to Jeremy.
The killer left no signs of break in/out, Jeremy would have had to let the murderer know how to do this.
The circles on the back are a very minor injury, and could well be as a result of a weapon already having been fired. Highly unlikely to be able to force Neville to do anything if the family are already shot.
The circles could be the result of something completely un-connected, they're certainly not torture inflicted, as they just aren't going to give pain.