If Sheila did it... Just want to run through what she must have done/not done based on the evidence.
Sheila's illness was a serious one. Despite an historical lack of violence to others, she 'flipped', killed her children, parents and finally herself.
Correct anything that is countered by evidence.
1) The gun - she must have wiped down the weapon prior to use. Two poor prints from Sheila and JB. Yet Neville used the gun all the time, and JB stated he used it the night before.
2) Put on gloves - (see prints on gun) plus no prints on the cartridges.
3) Kills family with gun and silencer - there is familial blood in the silencer, whoever it comes from.
a) 6'4'' Nevill puts up a sustained fight, but Sheila suffers no injuries, her fingernails are intact etc.
b) Boys' deaths demonstrate good recoil anticipation with a gun (purchased Nov 84) that no-one has
seen her use before. She has not been known to shoot in her adult life.
4) Removes silencer and places in gun cupboard.
5) Removes clothing (unless she carried out killings wearing only knickers and tights/leggings) and
gloves as these would be contaminated by blood and gun residue. Hides these items - never
discovered.
6) Removes and washes tights, hanging these over the bannisters. Removes knickers and puts to soak
in a bucket.
7) Washes all trace of blood and gun residue from her body. Removes all traces of blood from sink/bath
used.

Shoots herself. This is not immediately fatal. Shoots herself again.
Everyone happy?