Sure, Megumi discovers the truth about Toji being his dad in the manga. It's a crucial plot point that brings about various changes in Megumi's storyline and his relationships with others.
He might be shocked at first. In many fanfictions, Adrien would feel a mix of disbelief, anger, and sadness. He has always known his father as a strict but loving parent, and finding out he's Hawk Moth, a supervillain, would completely shatter his view of him.
Obviously, Charlie and Miles are the main characters. Charlie is the one who has the big discovery about Miles being her father. And Miles is the person who is revealed to be Charlie's dad, so he must have a big role in the story as well, with his own backstory and reasons for why this situation has come about.
Perhaps Charlie overhears a conversation that makes her suspect Miles is her father. In the fanfic, the story could then focus on how Charlie approaches Miles to confirm this. There could be a lot of internal struggle for both of them. Miles might be hesitant to admit it at first, fearing how it will change their relationship. Charlie, on the other hand, might be desperate for answers and a real connection with her father she never knew she had.
Another theme is growth. Megumi's growth as a person and as a sorcerer is often tied to his relationship with Gojo. In these fanfics, Gojo's influence helps Megumi become stronger, not just in terms of his abilities but also in his emotional maturity. For instance, Gojo might teach Megumi how to handle difficult situations, which in turn helps Megumi grow. And of course, the theme of love is there. It might not be a romantic love, but the love between a father and son. Gojo's care for Megumi and Megumi's acceptance of Gojo as a father figure is a central part of these fanfics. It gives a warm and fuzzy feeling to the readers.
I'm not sure about the name exactly, but there are some fanfics where Megumi calls Gojo dad in a more action - packed setting. For example, in some where they are fighting curses together. Megumi's respect for Gojo as a father - like figure is shown through their teamwork and how Gojo protects Megumi during battles.
For Merlin, there are both good and bad consequences. On the bad side, some of the more traditional and anti - magic people in Camelot might try to oppose him. However, since Arthur now knows, he has a powerful ally. Arthur can protect Merlin from those who would do him harm. Also, Merlin can now be more open about using his magic for the good of Camelot, which is a positive change.
I'm not sure if 'his wife is story' is a correct expression. It might be a misprint or an unclear statement. If you mean 'his wife is a storyteller', then it means his wife likes to tell stories. If it's something else, more context is needed.
Some of his other friends might react differently too. Some may be more cautious around him, worried about the power of the jinchuuriki within him. But those who truly trust Naruto, like Shikamaru, might not change their attitude much. They would see that Naruto is still the same person he was before, just with this added aspect to his identity.