Alex's sister is not integral to the plot by any means, but she may well appear.

Hopefully the story still manages to be interesting and hold attention. At times it feels a bit like I'm going into excruciatingly introspective detail about things and it drags, but I'm always trying to have something new, or some kind of info or a development each chapter that adds to the overall plot. Things are gradually being unveiled and revealed and it all helps keep Jack's perspective in a state of evolution - he doesn't know how the others think or truly act but as time goes on, that picture becomes more complete. It can be tricky to write but I think it's a lot more engaging than having an omnipotent narrator who says things like 'Alex wanted to save Jack but was panicking' or 'Penny wanted to kiss him very badly' - the eventual reveal of these feelings and the intent behind certain actions can be more satisfying, and closer to the human experience itself.

Interesting observations. Jack hasn't really had a proper conversation with Alex yet, for several reasons, so the reader still doesn't fully know what or who she really is. Who's to say if this will continue or not? As for Caitlin, you're right, she sure seems insecure about being seen as weak...