Actually the protocol problems they face do not stem from the fantasy. The heroine is queen at the age of seven, and while there's magic involved in that, and it complicates her life in other ways, it doesn't really affect protocol.
They are improvising. The young queen can have suitable entertainments for young people her own age. Which at the moment means young people who are suitable in rank for any sort of court entertainment, there being a dearth of children in the capital on account of no one expected it to be an advantage. But a boy is arriving with his great-grandfather, and it occurs to me that the other children could be presented by their parents, but the queen doesn't know the great-grandfather.
That could fixed by a little re-writing. More complex protocol issues would stem from actual fantasy issues. . . kings and queens have to be polite to wizards who were guttersnipes. Dragons and elves who claim seniority everywhere. The necessity of avoiding decor that will trigger a vampire's compulsive need to count if you actually want to invite him somewhere -- though, fortunately, you probably want to do that in a free-standing structure that doesn't count as part of the main building. It is in particulars of magic that the changes lie. Don't keep gold around when the necromancer arrives if it harms his skeletons. Arrange for werewolves to visit during the new moon. Smoothly slip from treating the youth as a gardener's boy to as a prince and the princess's betrothed when he stands revealed as the heroic knight who saved the kingdom.