I wouldn't have a heap of listen checks, I'd much rather have fewer checks but of more importance. 2 checks each, 1 for the lock and another for the sneaking. I doubt that the people in other rooms would even get checks, depends on the ambient sounds, i.e. socializing downstairs/late night street traffic/owl etc. The module probably takes this into account anyhoo.
The point as I see it is that the players seem to have been playing 7th level characters as if they were much lower level where they have less history and less enemies.
If the characters that got slaughtered were freshly made then I'd let it stand and get everyone to roll up. If they were veteren pcs then they were proberly overdue the tpk.