I... feel like I managed to convince at least one of them to change their ways so it wouldn't be as detrimental as they were before. Convinced them enough to work together with others like them instead of hiding away where they thought it was safe. It managed to help out in a battle, at least.

Don't you have the power to hold them accountable for disobeying those laws? Do you have some sort of guard or force that can be around to keep an eye on things? [Because of course one person can't be around to uphold the law in an entire kingdom, he agrees with that bit at least.]

If you've been king for that long and the people have followed you for all that time, why not show what you really are if you haven't yet? If you've been king for four years and you've been a benevolent ruler, then that's proof that the Deryni aren't automatically monsters, if you're one too.