The sister could have a big impact. Suppose she has a gift of reading minds like Edward. She might be able to tell if Edward has any hidden motives towards Bella. If she senses something wrong, she'll surely try to break them up. But if she approves of Edward, she could actually be a great confidante for both of them, and help them communicate better when they have misunderstandings.
I'm not entirely sure if there is a specific 'Bella has anorexia' Twilight fanfiction. There are so many fanfictions out there that it's hard to keep track of all the different themes. But given the nature of fanfiction and how it allows for creative exploration, it's very possible that someone has written about this. It could be an interesting, if somewhat dark, take on Bella's character.
Yes, there are likely many 'Twilight' fanfictions out there that could involve Renesmee having a sister. Fanfiction writers often come up with creative new storylines and characters. Some might explore what it would be like if Renesmee had a sister in the complex world of 'Twilight' with its vampires, werewolves, and unique family dynamics.
One common theme is family dynamics. Since it's about Bella's sister, it often explores how the sister fits into the family structure, especially with Bella being so central in the original Twilight story. Another theme is love triangles. Just like in the original, but now with the sister involved in some way.
No. In the original 'Twilight' series, Bella is a female character, and having such a theme goes against the established gender identity in the official story. It also might be considered inappropriate and a deviation from the general tone and concept of the 'Twilight' universe.
There could be other minor characters from Forks that get more spotlight in these fanfictions. For instance, the classmates of Bella's little sister who start to notice that there's something strange about her. They might become curious and start to dig deeper into the secrets of the town, which then draws in the vampires and werewolves.
I really liked a fanfic where Bella's twin sister was a werewolf. It added a whole new layer to the story. Instead of being drawn to the Cullens like Bella, she was more involved with the werewolf pack. It explored how she tried to keep her identity a secret from Bella at first, which led to some really tense and exciting moments.
A common trope is the twin having a different supernatural ability. For example, she might be able to control the elements while Bella has her mind - shield. Another is the love triangle, but instead of Edward - Jacob - Bella, it's between different characters involving the twin. Often, the twin also has a secret she's keeping from Bella which drives the plot.
Love and friendship are also common themes. The baby sister may find love among the supernatural beings or form strong friendships. For example, she could become friends with some of the werewolves while also having a connection with the Cullens. It adds a new layer to the existing relationships in the Twilight world.
Some fanfictions might introduce new characters that become popular. For instance, a new vampire who befriends the little sister. This vampire could have a different set of powers or a unique backstory that makes them stand out. Also, other members of the Cullen family, like Alice, could have a closer relationship with the little sister in the fanfiction, which makes her a popular character in this new narrative.