Kill Daniel & Nicholas while they slept.
Kill Nevill & June in their bedroom.
Maneuver Sheila into twins room.
Kill Sheila with one shot.
Move bedroom phone into bedroom (if not already there).
Move Nevill a few feet away from the bed. Unless he had already crawled, as June did.
Ring his AM from the bedroom phone (unconfirmed he did this).
Leave bedroom phone off the hook.
Remove & replace silencer in it's box (if he knew beforehand about it's lenght).