Yes, in the vast world of fanfiction, there are all kinds of creative and out - of - the - box stories. Some fans like to explore unusual relationships and scenarios, so it's possible that there is such a fanfiction out there. However, it goes against the original canon of the Dragon Ball series in many ways.
Well, if they were brothers in a fanfic, it could change how they interact with the other characters. Maybe they'd have a deeper understanding and fewer power struggles between them. Also, their family background and upbringing could be explored in new and interesting ways.
It's a bit hard to say for sure. Both Vegeta and Goku have their moments of strength. Goku has some unique powers and techniques that give him an edge at times, but Vegeta is no slouch either and constantly works to catch up and surpass Goku.
Generally, Goku still holds the edge over Vegeta. Their power levels fluctuate, but Goku often achieves higher peaks of strength and unlocks more powerful forms first.
It often starts with a shock or surprise at the mpreg situation. Then, they gradually learn to rely on each other more. For example, Vegeta might start to show a more caring side that he usually hides, and Goku might become more responsible. They'll have to communicate more, sharing their fears and hopes about the future with the baby.
The fanfiction might make their relationship more equal in a different sense. Before, there was always a bit of a power struggle between them. But as mates, they have to respect each other on a whole new level. They would have to consider each other's feelings and opinions more. For example, when making decisions about how to face a new enemy, they would have to consult each other rather than just going with their own instincts like they used to.
Many Goku and Vegeta fanfictions explore the concept of power. How they strive for more power, what they are willing to sacrifice for it, and how they handle having great power. This can lead to some interesting moral and ethical dilemmas within the stories.