Responses
Let's just simplify and say that her brother and mother are jerks and just didn't want to be related to people they think are inferior idiots.
I agree with her body being taken, but also... maybe she and kairak are reincarnations of a previous dragon and ryenas. And she probably did love him, but maybe it was that love that made like...world destruction? I mean the story does hint that she could've been the last human in a post-apocalyptic world with the big kairak no? well that's my theory anyway...
I think what her brother was hinting at was that Reana’s body was taken over when she was little, and therefore no longer his younger sibling. I think that her «former self» (the one who took over Reana's body) might have been in love with a version of Kairak or something? And that her former self maybe was a dragon?