beta
I’ve read the novels & my understanding is that the brother &sister are not blood related, but because she’s older she didn’t think he knew. It’s explained in the novel that she was from a previous marriage of the 1st wife of the ML’s dad(her stepdad).That is also the reason why she’s obsessed with being accepted by the father & inheriting the company. also why she is beta when everyone else in family are alphas.