That brother is a horrible creature when he's angry, and he needs to be informed of that immediately. And if he doesn't understand from being told, then make him talk to his sister and just listen to her. And if he doesn't understand after that, then unfortunately he is a person without any sense of responsibility for his actions.
And that woman is just as vile. She clearly doesn't need to steal and sell things in order to survive, and she certainly does not deserve to keep the money that she already has, either. They should fine her for every bit of money she was expecting to get from these ponies.