Well, Mary wont need to be the heir since she will be part of the new queen’s government... Alicia cant be so daft as not to notice with this last chapter that Mary knew all along what she truly was.
MC is a moron, who the hell cares about a family that treats you that way, the sister is also selfish, she knows he gets shit treatment and instead of being careful she is open about meeting him carelessly, also some things dont add up with the story...