It is quite a straight forward scenario after the kitchen fight -
Nevill was immobilised after his 4 shots & kitchen fight.
Bamber went straight upstairs to finsh everything off.
After shooting Sheila, the silencer was taken off. Which was either pre planned or Bamber realised at the time it needed to be.
After having to shoot June 2 more times upstairs, he decided to shoot Nevill 4 more times in the head.
Nevill was lifted and put onto the coal scuttle to give Bamber access to Nevill's head and bare back.
Nevill was shot and burned 4 & 3 times.