To summarize, everyone is on the Dessarin Road...your goal is to get to Rivergarde Keep on the opposite side of the great Dessarin River. Unfortunately the only crossing point is a trek out of the way, farther North to the Stone Bridge. You've learned of beautiful Dwarven books being traded and such by not-so-good intentioned people. These books belonged to one of the Delegation all of you are searching for. Heading north will allow you to investigate the delegation disappearance further. Perhaps you may find more clues on your way to Rivergarde Keep, and once you are there, discover more about this group that had the books.