Even the name Snow White sorta exists with names like Blanche. And the name Belle does exist as well as variants like Bella. The difference is that Belle and Snow White are pretty much exclusively tied to their own stories (excluding Snow White and Rose Red but the German name for that Snow White is different from the more famous Snow White's name in German. In the Disney movie, it's clear that the queen is angry with his betrayal but her more pressing issue is eliminating Snow White. I'll put this in spoilers in case you don't want to see it but another major change is we find out what happened to the Huntsman. For example, Snow White and the Prince have met way before the I'm Wishing scene where the Queen first seems them together. Yes, her books do mess around with story elements and even Fairest had this issue. I can't quite remember now but fans were not pleased. Ursula had a weird backstory in hers, like I think she was adopted or something by Triton's family.
And like I said, I'm not sure why it was necessary to give the sisters their own book because they pretty much dominate all the other ones. My headcanon is that Henry is the royal name he was given but Christopher was chosen as his middle name because his mother wanted it and Kit became the pet name his parents used, especially after his mother's death to remember her. I like Henry the most and I like the idea of Christopher being his middle name so that Kit is his nickname that his father calls him like in the live-action film (and Cinderella would call him that too). Charming came about because of the Disney Princess franchise and since Snow White's prince was called "The Prince," I guess they felt it would be too much to have two princes called called that. He was never referred to as Prince Charming in the original film anyway, just The Prince. Charming is just a bit generic as a name for me and it's more of an archetype anyway than what should be the name for an individual character. I also think Ferdinand sounds like a Spanish name probably because of Ferdinand the Bull but I don't think it actually is. Valentino has at least two more books planned and I think she's said in the past that she's likely to do one for Lady Tremaine so I imagine we'll see one for her soon enough. A lot of fans cynically pointed out that they didn't need their own spinoff book because Ursula and Maleficent basically were their solo books lol. Ursula and Maleficent's books are basically entirely about them, one of the OCs is the Beast's former lover before Belle, and now Valentino is writing her own book just for them. She has a couple of original characters who pop up in every book and are usually responsible for turning the villains evil, but the issue is that she gives them too much of a role. The problem with her other books is that they are barely centered on the characters they are supposed to be about. Fairest is the first one and I agree that it's the best. Serena Valentino's books are usually just called the Villains books.
Apparently Belle's part was glossed over anyway. The Beast's book had this weird retcon that Gaston was his childhood friend and that the Prince had a former relationship before Belle and all of this rubbed people the wrong way. The Maleficent book apparently had nothing to do with her and the Ursula book was similarly criticized. Fairest is the only one I've heard good things about especially since it was before the Twisted Tales started to be nothing about the actual character. The Twisted Tales and Valentino books have interesting premises but they tend to get mediocre reviews and a lot of complaints.
I didn't realize you bought this book, I assumed you had rented it somehow. I avoid Charles as a name for him though because I'm not a fan of how everyone calls Cinderella's (or Snow White's) prince Charming. Charles and Henry are two of the most common names in western monarchies so they both could be a good fit. I also avoid Ferdinand because it was a mistaken name for Snow White's prince for the longest time. I can't see him with the name Otto because I always think of the pet ferret Gothel had in Barbie as Rapunzel who was given the same name.