i just hope that in some chapters their parents will understand that it's okay for their children to be anything other than 'a proper noble lady & gentlemen' as long as it's something right & didn't bring harm to anybody. so that their children didn't have to deceive them forever, cause isn't great if the children also get support from their parents? (｡•︿•｡)
With the way Cain had been dealing with the prince's parents, I think he's done the key steps to also make sure their hidden growth can prove to their parents that they can do both as young children who kinda have little say against authority. The parents are as supportive as they can be, but as nobles, they don't want their kids to be "unlike a Noble" (like Cain's emotional outburts against the prince despite having a valid concern, or Diana showing signs of unreserved assertiveness that would otherwise cause mayhem).
It's not him only ever clearing obstacles, he reinforces self-control, consideration, empathy, and the innate positive traits Diana already has. He is still a siscon, still caught up in his own obsession to clear the future, and has so many weaknesses and Diana gets to be her own active agent in affecting Cain (like she's so precious and the message that children are a bundle of potential and possibilities is so heartwarming).
Besides, teaching her to show a facade fitd the nobility status (and a lot of the parent nobles in most fantasy stories...esp the "elegant and wise wife being secretly as skilled or even better that knights or were previously adventurers before being a noble wife"). Got me so excited that I was stunned by the "recommendation page".