Their relationship would likely become more intense. With a baby on the way, there's a new level of commitment. Damon might become more tender and less reckless, as he now has Elena and the unborn child to think about. Elena would probably rely on Damon more, trusting him to protect her and their future family.
One idea could be that they face challenges from the vampire and werewolf communities. Since their relationship was already complex in the show, this pregnancy could stir up more trouble. Another plot could be them trying to keep the pregnancy a secret while preparing for the arrival of the baby. They might have to deal with issues like finding a safe place to raise the child in a world full of supernatural threats.
Caroline would likely be a mix of excited and cautious. She's a bit of a romantic at heart, so she might see the potential for a new family dynamic. However, she also knows Katherine's past and would be on guard to make sure Katherine doesn't manipulate Damon during the pregnancy. She would probably try to befriend Katherine to keep an eye on things.
Damon might initially be shocked and angry. He has always had feelings for Elena, and seeing Stefan marry both her and Caroline could make him feel betrayed. He might lash out and try to cause trouble for their relationship at first.
Stefan would be extremely worried and angry. As Elena's other love interest, he has a deep connection with her. He would immediately start looking for her, using all his vampire skills and resources. He would probably suspect Damon right away, given their history of rivalry over Elena.
Elena would probably be terrified at first. She's a human in a world full of powerful supernatural beings. Being kidnapped by Damon would mean she's in a very vulnerable position. She might initially try to fight back or escape, using any opportunity that presents itself.
Stefan might be initially shocked but then be very supportive. He would probably offer to help in any way he can, like babysitting or giving advice based on his own experiences. Bonnie would be excited and use her magic to create some special things for the baby, like a protective charm.
I really like 'Klaus and the Unlikely Companion'. In this fanfiction, the OC is a witch who crosses paths with Klaus. What makes it stand out is the way it portrays Klaus's vulnerability around the OC. It shows a different side of him that we don't often see in the show. The plot twists are also quite engaging.
A 'a family affair tvd fanfic' could be about different family - related storylines. It might be about a family that has just moved to Mystic Falls and how they get involved with the existing families in the show. Or perhaps it's about a long - lost family member of one of the main characters showing up and causing chaos. It could also explore the family trees of the vampires and werewolves in the show, and how their family legacies impact their actions and interactions.