@SGR
The second document isn't just for the compensation from the engament breakage and the fidelity clause. It's also for the false accusations and defamation, from the violence (documented with a lot of witnesses)
1. Petty shit like a few hugs do not make infidelity.
I think that we agree on this one. However while hugs doesn't constitute an infidelity proof (but in the eyes of this kind of society certainly a blunder at best), starting defaming your fiancèe defending her certainly rise some bells. In noble society Infidelity can be overlooked, slandering someone reputation so publicly using clearly unsubsatial claim cannot.
2. Ultimately the contract is downright extortion and just unfair to the core. The actions of one family member destroy the family as a whole? And those actions being just adultery? BS.
I agree that is unfair, except isn't just for adultery. Ramon DEFAMED her, publicly and also did phsysical violence in one occasion.
These society often doesn't have a proper stance on personal responsability. It happenend on the real world where noble house fallen completly from grace for the action of one.
(Albeit for way more serious crimes, not for petty things like this).
4. Noble society does not view justice the way we do - through the protagonist's eyes. They see a Marquis house being destroyed on a whim to benefit a mercantile-oriented County. That is EXTREMELY suspect and will immediately lead to nearly everyone questioning the actions of the king in this. The titles and wealth are all they have. If the king can take out any of those on a whim - that is cause for worry to the point of rebellion.
While it's true that the memeber of noble society wouldn't have the same view on justice. The king doesn't just represent noble society but the country as whole. If the King wouldn't accept the Nogah could clearly use their foreign connections to lobby foreign merchants to interrupt the trade.
Take also in mind that the King clearly stated that he himself had doubt about the Curions work. And, as you say, he is certainly sharp, calculating and scheming, he probably took the chance to get rid of them. Albeit I think that is exaclty how you are saying, he will claim a compensation himself for this. The King and Queen may not be Nogah by blood, but are Nogah to the core de facto.
Then dunno, maybe the novel detail this sequence better, with more dialogues and details?
Also are you sure about them losing the title? They lost the home and the territory (along with the relevant assets), but their title isn't explictly mentioned (except pheraps in "They are not needed" phrase from the King). Unless losing the territory automatically downgrade them, but then the Nogah should have an upgrade, and it doesn't seem to happen.
So the family isn't dead.
However my main point was slightly different. If the King refused to sign the second document, after breaking the engagment, it would have been an injustice to the Nogahs. What I concede is that the King could step in and ask for a different settlement (using maybe the state or the royal family's money but this can cause another issue for the country at whole). Expecially after all the visual evidence they produced (yes producing this much of evidence is a clear signal that there is a scheme going on, but the evidence itself isn't forged/fake), is shown Yulia probably gained some supporters into the noble audience. Another possibility is for the king to outright refuse to break the engagment (possible only if the evidence isn't shown at all, or his reputation would suffer), but a compensation would be still required (for all the defamation etcetc), albeit inferior. Or yes the king can claim bullshit on the infidelity clause, linking to the date it's added, and make them settle with a reduced compensation. He cannot refuse to pay at all, not without suffering massive backlash.
P.S I disagree from the idea that the king is playing chess while Yulia checkers. I think both are playing chess, but Yulia a Petrosyan, while the king a Fisher or Carlsen. (The reference to Petrosyan is for his extremly solid playstyle, as Yulia and Co fortified themselves to blow the maximum damage while being well defenced, albeit there is still a risk that the entire fortress fall. (As sometimes happened againt Fisher himself))
hope that they will not amount to "I did this for you now you marry my son as payment". I hope... I wish... ... fuck it's going to be this way now, isn't it?...
I will be extremly disappointed