I was blind, but Azura's star has guided me through my dreams. Vivec's high priest, Saryoni, has asked to see you when you are Hortator and Nerevarine. Go to him, and demand to speak with the false god Vivec. Vivec has tried to keep Kagrenac's Tools secret, but you will need these tools when you stand before Dagoth Ur. Get Kagrenac's Tools from Vivec. They are the keys to the riddle of the Sixth and Seventh Trials.

I am not sure. "The tribe unmourned" may mean the Sixth House, House Dagoth, which was exterminated after the Battle of Red Mountain. But it may also mean the Dwemer, or the Dwarves, as Westerners call them. And "eating sin" is doing atonement for another's sin.