Many of the traps inside the Tomb will instant kill parties at level 5. Aside from my bewilderment they're still only level 5 after travelling that whole way, I mean did they go in a straight line?? Assuming they went to maybe 5 landmarks on the way and had maybe 30 fights on the way here.. math isn't working out.

Three choices: retroactive levels to at least 7, half the damage of the traps in the Tomb (do not recommend), or get ready for a lot of death even more than normal. I'd most advise considering where you went wrong (seeing as how there is a recommended levels chart at the start of the module) and admit to your players you made a mistake and have to fix it somehow.