Harsh. But yeah the father with his lack of aptitude and backbone, has ruined both his family and country. The new queen has rotted the country from within, making a pact with demons posing as assasins (if i remember well, the female demon that he fought he identified as the blind maid following the queen) and he and his half-siblings don't trust his father to keep the queen in check.
And MC is aiming much higher than being a king of a small country.