Well, one interesting plot might be that Bella accidentally stumbles upon an old diary of Sam's that reveals his past insecurities and dreams. She decides to help him fulfill some of those long - forgotten dreams. Another could be that they both get transported to a magical realm and have to rely on each other to find their way back home. This would involve them using their unique skills and the bond they have as siblings. And a third idea is that Bella is bullied at school and Sam stands up for her in a really heroic way, which changes the way the other kids view them both.
One idea could be that Sam and Bella discover a hidden magical realm together while on a hike in the forest. They have to work together to find their way out and in the process, they learn more about each other's fears and hopes.
One idea could be that Bella discovers she has special powers because of her relation to Sam and Dean. Maybe she can communicate with spirits in a unique way that helps them on their hunts.
One idea could be that they face challenges from their families. Maybe Bella's family is initially shocked and has to come to terms with the situation. Another could be that they have to deal with the gossip in their small town. For example, people might spread rumors about how it all happened so quickly.
One plot idea could be that Sam and Bella are married but have to keep it a secret from their families for some reason. They then have to navigate their relationship while hiding it. Another could be that they get married quickly and then have to learn about each other's quirks and habits in their married life.
One idea could be that they discover a long - lost family secret together. Maybe there's a hidden inheritance or a special power that runs in the family that only they are destined to uncover.
One idea could be that Bella's sister discovers a hidden power within herself. Maybe she can communicate with animals and uses this ability to protect the town from an unknown threat.
Another plot could be that Sam's sister falls in love with a character from a different faction in the Twilight universe. This would create a lot of tension as their relationship would be frowned upon by both of their respective groups. It could explore themes of forbidden love and loyalty, as she has to decide between her family and her newfound love.
One idea could be that Hermione uses her intelligence to help Sam out of various tricky situations at school. For example, when Sam gets into trouble with a difficult teacher, Hermione devises a clever plan to get him out of it. Another plot could involve Hermione introducing Sam to the wizarding world, and Sam having to adjust to all the strange new things like magic spells and magical creatures. It could also be interesting if they team up to solve a mystery in their town that has both muggle and wizarding elements.
One idea could be that Harry's little sister discovers she has a unique magical power that no one else in the family has. Maybe she can communicate with magical creatures in a way that even Hagrid is impressed by.
One plot idea could be that Bella's sister discovers she has a special power as a vampire, like being able to see the future. This could lead to her trying to prevent bad things from happening to her family and the Cullen family. Another idea is that she struggles with the morality of being a vampire while also being in love with a human. She might try to find a way to exist without harming humans, which would create a lot of internal conflict.