Following Sint's law does not require any "forced conversion" or beheading. As a noble of Sint, Victus could easily have read the realm laws and known that. All Ralina ever asked for was that priests of Hemaism be allowed to preach in any region aligned to Sint. After all, Victus was obviously using his position as Duke of Heen to spread his faith in the new duchy, in order to make sure his religion was firmly established to the exclusion of all others. It was a bit of a dual standard, or something, for Victus to us the authority of the treaty to attempt to claim Ducal authority over regions of the new colony, some of which were not even in his duchy, and yet deny defering to the duke who was specified by the treaty to actually hold that authority. Because Moonglum, being a Hemaist, would of course allow Hemaist priests to preach in the duchy of Heen. But that would endanger Victus' plan for religious domination of the new colony, which he has been pursuing since the day he arrived in Sint.
And your definitions of throwing a fit? It seems like you think anyone that doesn't march in lockstep with your demands is throwing a fit. Ralina and Cyprian both had very mild responses to Victus' actions. All Cyprian did was send a copy of the treaty and ask for calm and discussion. (To which Victus never responded, and instead seceded the duchy with further letters.)
In fact, the only one who could possibly have been considered to have had a fit would be Victus himself.
This is going to be one very interesting realm...