One common plotline is how they deal with the reactions of their families and friends. Since their relationship might be unexpected, it can create a lot of drama. For example, Elena's friends from her original circle might be skeptical or even hostile at first.
Elena's friends and family might be a bit wary at first. After all, Elijah is from a different world. Her aunt Jenna might be concerned about the implications of this marriage for Elena's future. However, her friends like Bonnie and Caroline could come around once they see how much Elijah loves Elena. For Elijah's family, some might be happy to see him find love, while others, who are more traditional or power - hungry, might see Elena as an outsider and try to break them up.
You can try fanfiction websites like Archive of Our Own (AO3). There are a lot of talented writers who create fanfictions about Elena and Elijah getting married. Just search for their names on the site, and you'll get a bunch of results. You can also check out Fanfiction.net, though AO3 generally has a wider range of more modern and diverse works.
One possible plot twist could be that a long - lost relative of Elena shows up to oppose the marriage. Maybe this relative has some ancient grudge against the family that Elijah is from. Another twist could be that a powerful witch casts a spell on Elijah, making him forget his love for Elena right before the wedding. Then Elena has to go on a quest to break the spell.
Well, first of all, Elijah would be by Elena's side all the time. He would help her with her daily needs, like getting things she needs or helping her move around when she becomes less mobile during the pregnancy. He would also share his knowledge of the supernatural world with her, so she can better understand what might be happening to her and the baby, and together they can prepare for any challenges that might come their way.
I really like 'Elena and Elijah's Uncharted Journey'. This fanfic takes them on an adventure outside of Mystic Falls. It has a lot of great dialogue that makes their connection seem very real and deep. The author does a wonderful job of building the story around their relationship.
Love is a very common theme. Their relationship, whether it's a budding romance or a deep platonic love, is often explored. Another theme is the idea of sacrifice. Given the complex situations they are often in, one or both may have to sacrifice something for the other.
A fanfiction could explore the idea that Elijah's desire for Elena is part of a bigger prophecy. Maybe there's a hidden message that says if Elijah and Elena are together, it will bring peace to the vampire and human world. So he's driven by this sense of duty as well as his personal feelings for her. This would lead to a lot of internal conflict for Elijah as he tries to balance his feelings with the potential consequences of their relationship.
One idea could be that Elijah tries to court Elena in a very old - fashioned and gentlemanly way. He might take her on trips to historical places he has known over the centuries, sharing his stories and knowledge with her. This would be a contrast to the other vampires' more aggressive approaches towards Elena.
Another theme is loyalty and betrayal. Given their complex relationships and the world they live in, there are often situations where loyalty is tested. For example, Elijah's loyalty to Klaus might be put to the test because of his feelings for Elena. And vice versa, Klaus might feel betrayed if Elijah gets too close to Elena.