The Drunken Lizard Pub

I searched every where I could reach/access in the sewers of kuudad, and
solved the 3 chest puzzle, and killed the assassin who killed my fellow guild
member, but I cant find a way to reach the other assasins there-though I
can see them, please some help, I dont mind spoilers.

It's part of the stairway puzzle. You have to search the buildings in the southeast part of Port Kuudad for ways onto the stairs to go up and then down.