Becky’s answer to “so why did her brother and mother hate marianne so much? i felt it was never explained.” > Likes and Comments

I completely agree. I think the answer is that her family is quite messed up in some way or another overall. However, the lack of a more detailed explanation for this took away from the story - a missed opportunity, in my opinion, that would have given more depth to story outside of just Marianne and Connell.