Honestly, his brother like someone said, may not like his family but still thinks of them, it's just he doesn't seem to realize that his sister was jealous of him and his relationship with their dad, and he's the kind of moron who blames her for the prince constantly cheating on her...and he's a stalker, but he isn't exactly coming in to kill his family.
I am pretty sure, though, that he is only at the house because the prince demanded him to go there and tell his sister not to break their engagement and remind her that she loves the prince, and the brother may just be annoyed at having to do this, probably because he is certain this is just another stupid tantrum from his sister.