I prefer to take Julie's version of events:that it was Jeremy who broached the subject of fostering that night to provoke Sheila,that Sheila may have retaliated in some way verbally and later wrote "I didn't mean to be horrible to Jeremy" in her diary,that Jeremy hired a proxy killer(who was really Jeremy in a balaclava) who made a telephone call from White House to his answerphone at Goldhanger,that Jeremy had lost control of himself somewhat that night and given Nevill more of a thrashing than he intended,but "the old man put up a good fight..".
We know Julie is telling the truth because she relates the bit about a glove coming off in the fight with Nevill,which none of the newspapers reported at the time. Jeremy didn't want a combination of his and Nevill's fingerprints on the murder weapon so they all had to be removed,to be replaced by a solitary fingerprint of Sheila's and a couple of Jeremy's,whereas if Jeremy had been shooting rabbits his fingerprints should have been all over that gun.along with more of Sheila's,who would not have wiped the gun in a state of paranoid psychosis.