They would become even closer. The shared responsibility of having a baby would strengthen their bond. Eddie would be more protective of Venom, and Venom would be more gentle towards Eddie, knowing they are in this together for the sake of their future child.
Some fanfictions might take a comical approach. Picture Eddie and Venom trying to live a normal life in the city, but Venom's lack of understanding of human customs leads to all sorts of hilarious situations. Eddie has to constantly explain things to Venom, like why you can't just eat people's pets or why it's not okay to jump from building to building in broad daylight.
One possible plot could be that they face a lot of challenges in preparing for the baby. Maybe they have to find a way to keep the baby safe from Venom's enemies. They might also struggle with how to raise a half - human, half - symbiote child, like figuring out what kind of diet the baby would need.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions, and you can easily search for Eddie Brock x Venom ones. Just use the search bar and type in the relevant tags.
Well, perhaps in the fanfiction, Spider - Man is tricked into becoming Venom. A villain could manipulate the situation so that the Venom symbiote attaches to Spider - Man. As Venom, he starts to see the world from a different perspective. His relationships with his friends and family become strained as they don't recognize the changed Spider - Man. He has to find a way to break free from the symbiote's control while still using its power for good.
His appearance would change drastically. As Venom, he would be taller, more muscular, and have a menacing look. His costume would be black with the big white spider logo. Also, his relationships would be affected. His friends might be scared of him, and he might have to prove that he is still the same person inside, despite the exterior and some personality changes.
One possible fanfiction could be about Venom finding its way into the Spider - Verse. Maybe it starts when a symbiote experiment in an alternate dimension goes wrong and Venom is accidentally sent into the Spider - Verse. He could encounter different versions of Spider - Man and create chaos as he tries to find a way back to his own dimension. He might initially be seen as a threat by the Spider - People, but as the story progresses, they could realize that he's just lost and confused.