I am new here and not sure if this has been presented as a theory, but is it possible that Hannah and Scratch are the same person and that Kalani and Hannah are Father and Daughter
Here is where my idea comes from:
We assume (suspect) that Kalani was one of the Mallers, (he may or may not have had a change of heart later on). I am assuming that Kalani lied about where he came from or at the very least how he went from pre zombie apocalypse location to Arena. I am also assuming that he was the betrayer to the Mallers (Bill never made sense to me because he always seemed like the guy who didn't want anyone in the building, not just Michael and his group, so why would he invite the Mallers).
Before Kalani crashed the helicopter he told Angel to grab the photo of Hannah saying "She was my Hannah". Which may just be a simple indication that the girl in the picture is "Hannah" or that someone within one of the known groups is Hannah.
Angel also seems to show some recognition when he see the photo of Hannah, showing that it is at least someone Angel knows, and that the group might known.
These are just a few ideas, I am happy to discuss further, but in my current Nyquil induced state of sickness I am not as eloquent or cognoscente as I was when I first came up with this theory.