Edward and Bella could be important characters. As Renesmee's parents, they would likely be deeply involved in the situation. They might be worried about her well - being, try to protect her from any threats related to the pregnancy, and offer their support and advice.
The Volturi could potentially be important characters. Their strict laws and power in the vampire world could mean that Renesmee's pregnancy violates some of their rules. They might show up to investigate or try to enforce their will, which would create a major conflict in the fanfiction.
Definitely the Cullens, especially Bella and Edward as Renesmee's parents. Also, Jacob who has a strong connection to Renesmee. And of course, the Volturi leaders like Aro, Caius and Marcus.
I'm not sure if there is a specific 'Jacob gets Renesmee pregnant' fanfiction. Fanfiction can cover a vast range of ideas, but this is a rather controversial and unusual plot. It might exist in some corners of the fanfiction world, but it also goes against some of the original concepts in the source material. You would need to search through various fanfiction platforms like Archive of Our Own or FanFiction.net to find out for sure.
The implications would be significant. First, it would change the entire perception of the characters. Jacob and Renesmee's relationship has certain boundaries in the original. This fanfiction concept would break those boundaries and create a whole new set of relationships and family dynamics. It might also face a lot of criticism from the fan community for straying too far from the source material. Additionally, it could raise ethical questions about the nature of the relationship depicted in the fanfiction, as Renesmee has a unique origin in the original story.
Another plot twist could be that the pregnancy progresses at an extremely abnormal rate. This could put Renesmee's life in danger and force her and her loved ones to find a way to slow it down or deal with the consequences of a very rapid development. It could also lead to some unexpected revelations about her own nature and abilities.
One of the main supporting characters could be Bella. As Renesmee's mother, she would likely be very involved in the pregnancy, offering advice and support. Another could be Edward. He might have some concerns about the situation but also be there to help protect the family. Alice could also be a key supporting character, perhaps using her gift to foresee any potential problems during the pregnancy.
It could be another hybrid like herself. Maybe there's a new character who is also part vampire and part human, and they fall in love and conceive a child.
Also, any friends that Renesmee has made throughout her life could be involved. They might be there to offer moral support, or there could be some who are jealous or envious of her situation, which could add some drama to the fanfic.
Maybe a human who has discovered the existence of vampires and wants to use Renesmee to prove it to the world. They might think that by kidnapping her, they can expose the vampire world and gain fame or fortune. Another option is a rogue werewolf who doesn't like the alliance between the vampires and werewolves and decides to take Renesmee as a way to break that bond.
The fanfiction could revolve around Renesmee's discovery of her pregnancy. She might initially be in shock or disbelief. Then, as the story progresses, it could detail how she starts to make plans for the future. There could be a lot of internal monologue about her hopes and fears for the child, and how she wants to raise it differently from how she was raised, given her unique situation.
Percy would probably be an important character. He's Annabeth's close friend and love interest. His reaction to Annabeth getting her period could be interesting, like he tries to be supportive but is a bit clumsy at first.