Well, Percy has seen a lot in his adventures. At first, he might be a bit taken aback because fanfiction is a whole new world compared to his real experiences. However, as he realizes that it's just fans exploring different scenarios with the characters, he could become rather indifferent. He might even start to see the value in it, as it shows how much the fans care about the overall story and its characters. He might think it's a little strange that people are so interested in writing about Nico and Will's relationship, but he'd respect the creativity of the fans.
He would probably be very displeased. Snape has always been strict and traditional, and fanfiction about the DA, which was an unauthorized student group in his eyes, would seem like a frivolous and inappropriate thing to him.
He might be quite shocked at first. After all, Wolfstar involves his dad's best friend Sirius and his other dad figure Lupin. It's a rather strange concept for him to think about them in a romantic way as he knew them in a different context.
Artemis would probably be furious. As a goddess associated with protection, especially of women and girls, she would see this as a great injustice. She might immediately start planning revenge on the one who did this to Percy.
Cedric would be deeply troubled. In the wizarding world, they have their own code of honor and respect. Finding out about Harry's abused fanfiction would go against everything Cedric stands for. He might start to question the morality of the Muggle world that allows such things to be written. He would also feel a sense of sadness for Harry, knowing that someone out there has created a story that portrays him in such a negative and harmful light. Cedric might even consider taking some sort of action, like talking to Harry about it or trying to get the fanfiction removed if he could, though that would be a complex matter given the nature of fanfiction and the different worlds they live in.
In some fanfictions, Snape might be secretly sympathetic. He may see the scars as a reminder of all Harry has been through, which could soften his usually harsh attitude towards Harry, at least for a moment.
She might be quite surprised at first. Fanfiction often takes the relationships of the characters in unexpected directions. Molly is a rather traditional character, so she could be a bit taken aback by some of the more creative interpretations in the fanfiction about Ron and Hermione.
Well, this is a really tough situation. The son could initially feel a sense of betrayal. His view of his mother would be completely shattered. He might also worry about how this could affect the family's reputation. He would likely need a lot of time to process his feelings and figure out how to deal with this new knowledge.
Naruto might be super excited. He loves making new friends, and a toddler would be like a new little friend to him. He'd probably start showing off his ninja moves to make the toddler laugh.
Well, Sirius would have a complex reaction. On one hand, he was very close to James, and his brother was Regulus. The idea of them in a romantic relationship in fanfiction would be hard for him to wrap his head around. He might start to question how people could come up with such a thing. He might also be a bit protective of James' memory, if he thinks the fanfiction is portraying James in a way he doesn't like. However, he might also be secretly a bit intrigued, because it's such a different take on the relationships he knew, and it might make him think about James and Regulus in a new light, but he'd never admit it out loud.
Charlie may initially be confused. Fanfiction isn't something he might be very familiar with. But once he understands what it is about Harry and Ginny, he might just shrug it off. He's got his own life with dragons and such, so he might not really care all that much as long as it doesn't cause any real - world problems for his sister and Harry. However, if it spreads some false or unflattering rumors in the wizarding community, he might get a bit annoyed.