Another aspect could be related to Renesmee's powers. If she discovers new abilities and uses them in a way that Edward thinks is dangerous or irresponsible, it would surely cause tension. He is used to being in control and having a say in how things are done in their family, and this newfound power of Renesmee's could disrupt that.
One possible reason could be Renesmee's growing independence. As she matures, she might want to make her own decisions which could conflict with Edward's over - protective nature. For example, she may want to explore the world more freely, while Edward, fearing for her safety, tries to restrict her.
One possible reason could be to create shock value. Writers might want to break the expectations of readers who are familiar with the loving relationship between Edward and Renesmee in the original 'Twilight' story. By creating such a dark and unexpected scenario, they hope to grab the attention of readers who are looking for something different from the usual fanfiction.
One possible reason could be power struggle. Jude has always been a fighter for power in the faerie world and Cardan is a prince. Their different standings and ambitions might lead to a fight. For example, Jude might see Cardan's actions as a threat to her own power or influence among the faeries.
One reason could be that he doesn't like how some fanfiction writers misinterpret his character. They might make him act in ways that are completely out of character in relation to Renesmee. He has a certain image of himself and his relationship with her, and fanfiction can mess that up.
One possible reason could be their rivalry over a love interest, like Bella. Jacob loves Bella and Edward is in a relationship with her. This love triangle often leads to tension and could easily erupt into a fight.
One reason could be their different outlooks on the Cullen family's future. Edward may have ideas that Rosalie disagrees with, like how involved they should be with the outside world or other vampire clans. Rosalie might be more concerned about protecting the family's status quo and secrecy, and Edward's actions could seem to her as jeopardizing that.
One reason could be a misunderstanding about their family's future. Maybe Edward has a vision of how the family should evolve that Carlisle disagrees with. For example, Edward might want to expand the family in a different way than Carlisle.
It could be about a misunderstanding. Renesmee might think Bella is being overprotective in a wrong way, like not allowing her to have normal relationships with others. This misunderstanding can escalate into a fight as Renesmee rebels against Bella's restrictions.
One reason could be Edward's overprotectiveness. He might try to control Bella's actions too much in the fanfiction, which could lead to her feeling suffocated and result in a fight. For example, if he stops her from seeing her human friends often.
One possible reason could be Edward's overprotectiveness. He might restrict Bella's actions too much in the fanfiction, which could lead to her feeling suffocated and result in a fight. For example, if he doesn't let her go out with her friends or participate in certain normal human activities.
There's also a possibility that a third party, like Bella, would step in and mediate. She would help them see each other's points of view and find a compromise. After all, Bella has a special connection to both of them and could use that to defuse the situation.