I'm actually using both those texts for my speech! So far from what I have done I focused on a cultural theme but also a bit about conformity.
I'm thinking to use the novel "Skin" by Adrienne Maria Vrettos, where the character is rejected by everyone at his school, an outcast, and furthermore there is a disconnection between the members of his family because his sister develops anorexia causing problems in the family, and his parents are always fighting. I guess a pretty straight-forward theme about not fitting in with others. I think maybe it's not "deep"/complex enough?
That is fine for the main theme. I haven't read that novel so I can't really help. Sorry.
Other themes you should consider, which are interwoven with people, place, time, context, etc, in depth for complexity and specific types of belonging are:
- Choice for individuals and groups (Came up in my HSC this year and was laughing, since it was a main theme for me)
- Memory, which may be common or lacking for an individual or a group (a family or community)
- Identity, which may lead to one's isolation/rejection or acceptance
- Ideas, which can be common between people allowing them to belong or a lack of common ideas may lead to rejection/isolation.
There are a few others that I can't think of at the moment. Good Luck with the speech.