So Jeremy Bamber indulges in many wild shots to implicate Sheila and leaves victims able to try to defend themselves.
Sorry, not getting this.
You are right on this point. Bamber planned to take everyone out with head shots whilst they were asleep. He succeeded with the boys, partially succeeded with Sheila, but almost failed with his parents who must have been awake, aware that something was amiss and so became moving targets making themselves more difficult to hit. Hence the wild placement until they succumbed as a result of the initial injuries - then four to Nevill's head in the kitchen and two to June's head in the bedroom. Nevill being forewarned that his life was in danger and stronger than June was quicker to react and attempted to make his way downstairs to escape the volley of shots, call for help from the Foakes family in Pages Lane, or find another weapon to defend himself with. This is the most logical and reasonable sequence of events.