OK, I've tried asking around the interwebs and have no other place to go.
I started a new game and rescued Serana. While I had her following me and I was "taking her back home", I may have done a few side quests. Having 2 followers. Kind of fun actually. However, now when I try to start conversation with her, she gives me short preloaded responses. I haven't done the "bloodstone chalice" mission yet. Could this be why?
Also, if I jump ahead in the game and do the Dragonborn missions to learn the "Bend Will" shout, could this work on Alduin?
Please check though the other comments and the all dates (bottom left of comments) this thread had been inactive for over two years old (and Bend Will not working on those two was mention). For the still unanswered question about Serana at that point of the main Dawnguard quest she's not a follower yet.