One interesting plot idea could be a love triangle where both Edward and Emmett are vying for Bella's attention in a more complex way than in the original story. Maybe there are external forces at play that make Bella question her feelings for both of them.
Another plot could involve Emmett and Edward having to team up to protect Bella from a new and powerful threat that is not part of the original Twilight lore. This could lead to some really interesting character development as they put aside any differences they may have had. For example, Emmett's more brash and physical approach might clash with Edward's more brooding and calculated one at first, but they learn to work together effectively. In the process, Bella could also discover new aspects of both of them, which could change the dynamics of their relationships.
One plot idea could be that Bella and Emmett decide to start a family, which is quite different for vampires. They might explore ways to have a child in a vampire - human hybrid way. Another idea is that they get involved in a vampire - only Olympics - like event where Emmett showcases his strength and Bella uses her unique skills. They could also face challenges from other vampire clans who don't approve of their union.
One interesting fanfiction could be about an alternate universe where Bella has to choose between Edward and Jasper in a more complex situation involving Emmett as a mediator. In such a story, the dynamics between the characters can be explored in depth, with their different personalities and abilities coming into play.
One idea could be that Edward is a criminal on the run and Bella, a journalist, is trying to expose his crimes but ends up falling in love with him. Another could be Edward as a criminal mastermind who recruits Bella into his world of crime. Maybe Edward is wrongly accused of a crime and Bella helps him prove his innocence while they face many dangerous situations together.
Well, perhaps in this fanfiction, the shower is a place where they find a magical or symbolic element. It could be that the water has some sort of special property that helps Edward control his thirst for Bella's blood in a new way. Or, the plot could revolve around them getting into an argument in the shower, which then leads to a passionate reconciliation as they realize how much they mean to each other and how they need to communicate better.
Perhaps in the fanfiction, Bella is also in prison for some unjust reason. Edward, being a vampire, has to use his special abilities secretly to protect her from the other inmates. He could be using his mind - reading skills to anticipate threats.
A plot could involve Renesmee's love life. Since she is a special being, finding a suitable partner would be difficult. It could be a story of her falling in love with a human who is initially afraid of her but gradually comes to accept her. Edward and Bella would be there to guide her through this new experience, while also being protective. Or perhaps a plot where Renesmee discovers a hidden power within herself that has been passed down from an ancient vampire ancestor, and she has to learn to control it with the help of Edward and Bella.
Maybe a plot where Renesmee has to face some sort of vampire - human conflict that her parents once faced, but in a different context. Since she is part - vampire and part - human, she could be a bridge between the two worlds and strive to bring peace. She could use her understanding of both sides to defuse tense situations.
One idea could be a story about how they deal with a mysterious threat to their kingdom. Maybe a dark sorcerer is causing problems and they have to use their combined wisdom and courage to defeat it.
One idea could be that they go on a secret adventure outside the palace grounds. They discover a hidden magical forest that is filled with strange creatures. They have to work together to find their way back home and in the process, their relationship deepens.
Another plot idea could be that Bella starts to have strange dreams during the honeymoon. These dreams seem to be prophetic, showing her glimpses of their future together and some potential threats. Edward tries to comfort her and figure out what these dreams mean, which could lead to a deeper exploration of their relationship and the Twilight world.