Crew rest areas are either above or below the main deck dependant upon a/c type.
747s are accessed by steps adjacent to door 5 left and are above the cabin whereas, where fitted, A340-600 are accessed through a hatch in the floor beside the rear galley. The hatch is in what looks like a cupboard.
A340-200 has the capability to carry a crew rest pod in the rear hold. This is connected electrically and again accessed from the main cabin. BA 777 crew rest area is above the cabin midships.
The configuration of crew rest areas varies between companies.
A coffin would most likely, but not definitely, be in the rear 'bulk' hold and would therefore not be accessable from the cabin. If it was carried in either main hold it would be in a container or netted down on a pallet.
Hope this helps.