This author doesn't know how to politic. The reasoning behind why the king thinks his daughter has to marry the douchbag is stupid. That guy's own family should have disowned him ages ago, after it became known he killed his own wives, or at least put him under house arrest or sent him away to "study abroad", as was the usual thing you did when handling undesirable heirs.
The author seems to think that the Douchebag being part of some powerful family guarantees that other nobles would join him in a civil war, but in reality his conduct would have tarnished his own family's reputation, and he'd be a single rebel acting out… Influential families don't stay powerful simply for no reason…