I know it is always a bit of gamble to talk about characters when you still are missing some details about their life. However, there are a few things about Reiner and Bertholdt that I have been thinking about for a while now.
I want to start with Reiner. It is established in vol 11, that Reiner at times showcases behavior, and lines of thought that are contradictory. Why would a person who`s mission was to destroy the wall, suddenly start talking about the residents of the wall in a caring manner? Reiner himself does not even recognize this at first.