@thegrimlich The issue of Julius' culpability in assisting Gaius in violating the declaration is actually the easiest one to throw back at the others. To prevent Gaius from attempting his gambit would have likely required staging a coup to remove his father by force, almost certainly killing him in the process. In other words, the others are effectively disparaging Julius for having failed to rise up against his liege and his own father. If that's the case, the comeback to that is simple, how easily can Souma or Jean decide to raise their sword against their own loved ones just because they were doing "wrong?" What right do they have to demand that he commit patricide, regicide, and treason on their behalf?
As for satisfying the Empire, there's no point in trying. The Empire is pissed, and nothing Julius can do is going to appease them. That being the case, he might as well extract as much usage out of them as possible in the here and now. The Empire wants the declaration to stand, so Julius should have framed the entire intervention solely in a manner to paint Amidonia as having been compliant the entire time. Yes, that declaration is so meaningless that one can bend it into whatever sort of pretzel one desires to actually do that. The more widely publicized those flaws are, the weaker the symbolic value of the declaration, and the more the Empire has to commit cold, hard steel to prop it up. Seeing as frankly at this point Julius has little to lose, he should have just held the declaration hostage outright and dared the Empire to risk it becoming completely invalidated. Could that blow up in his face and see him dead? Of course. But the losses inflicted upon Amidonia at this point were functionally a deathblow anyway, even setting aside Souma's later plans. Does the Empire consider building cordial relations with the kingdom worth the effective dismantlement of the declaration?