Read Brothers of Cinderella Manga:
Joyce has a loving family, but after her father's death, her stepmother and stepbrothers turn abusive. So, what's a girl to do? Escape, of course! Then, one night, her stepbrother finds her with an indecent proposal—seduce Prince Charming or watch as the one she loves dies?!
Now, she must endure rigorous training to become the prim and proper lady Prince Charming will love.