But all JB had to do was leave the silencer beside Sheila Steve? I am not suggesting he take it with him away from the crime scene, where it may have been noticed that it was missing?
That is you view.
He probably took it off downstairs prior to burning Nevill's back. So just put it back in it's usual place.
As said he would not know about back spatter or that the silencer had scratched the aga.
He certainly would not be expecting the relatives to be suspiscious & given access to WHF.
All straight forward.