To those wondering the contradiction of the trashy parents, it's cause they aren't thinking JUST about the marriage with the prince. They want her to be this "perfect" empress. Their abuse is what led to Lizzie brainwashing herself into being this puppet whose sole purpose for existing is to become this "perfect" empress. All they are seeing is children playing. They likely are looking at how Lizzie got dirty playing and such, and thus see it as a disgrace to their family.
In other words, they deserve to die a miserable death. That or they deserve to be stripped of status and made into peasants, which they would see as a fate worse than death.