So I may have dug myself into a big of a hole here. I've been GMing for a while now, but mostly Pathfinder Society and Homebrew stuff. I've only ever played one AP, but am going to be starting RotR soon for my group. The problem I've come into is that my party is going to be starting at level 3. They're from the town of Kassen and they will soon complete the module "Crypt of the Everflame", and I have plans to take them through the two sequels to it, Masks of the Living God, and City of Golden Death, modules tiered for a level 3 party and a level 5 party respectfully, though Golden Death is suppose to be incredibly difficult from what I understand, Masks seems to be of a role play module from my experience.
My original plan was to hold off on the two modules till after the completion of book 1, my party isn't very power built (Rogue, Cleric, Sorcerer, Barbarian, Samurai). We've been doing everything on the fast track. My major concern is that I'm worried they're going to cakewalk through the first book, if I have done my math correctly, they'll be about halfway between level 5 and level 6 by the end of it. What I'm trying to do is toughen up the first book a bit but would be open to suggestions. Any help would certainly be appreciated.