Kingdom of Knuffel

It's about a girl. Her father is a rich landowner. She has one brother. She is close with her father and knows about their land - who lives on it, what everyone does, what everyone pays for rent, etc. The brother is closer with the mother and doesn't care for being outside or learning about the land. The girl assumes she will always live there. But, as she gets older, she realizes she will be pushed out and will be forced to marry some rich man somewhere else. She starts sleeping with a poor buy her age who lives on their land. Her brother becomes sort of infatuated with the boy. So the boy suggests they kill her father. Then the brother will inherit, now while he's young, and stupid, and infatuated, and has no sons to inherit. Then they will cheat him and steal from him until he has no choice but to sell the house. They will then use the money they stole from him to buy the house and get married.