His father might be extremely proud. After all, Goku has achieved so much, like protecting the Earth multiple times. He would look at Goku with admiration for his strength and kindness.
It's fairly common. Fans often look for more content related to their favorite shows. Since 'Attack on Titan' has a large and passionate fan base, there are a lot of fanfics available. 'Aot' fans might watch (read) these fanfics to explore different scenarios that the official story didn't cover. For example, they might want to see how a certain character would react in a different situation or what would happen if a major plot event had a different outcome.
Gohan would be really surprised, but being the kind - hearted person he is, he would try to understand and help out. He could offer to train with them in a more gentle way to keep them fit during the pregnancy. Piccolo would be more of a silent observer, but still be there in case of any threats.
The reaction among fans would be quite mixed. Some die - hard fans of the original series would be appalled as they have a clear image of ChiChi and Goku's relationship. They would see this type of fanfiction as a perversion of the original concept. On the other hand, there are those who are more open - minded and might see it as an interesting, if not controversial, exploration of the characters. But overall, the negative reactions would probably outweigh the positive ones.
Goku would be a mix of angry and worried. His Saiyan blood would make him want to rush into battle with Raditz right away. But he also knows how dangerous Raditz is, so he might first try to gather some allies, like Piccolo. He'd be constantly thinking about Gohan and how to rescue him as quickly as possible.
Goku would likely be extremely excited. He has always had a longing to know more about his Saiyan heritage and his father. Meeting Bardock would be like a dream come true for him. He'd probably ask a million questions about his past and Saiyan culture. Chi - Chi, on the other hand, would be a bit more reserved at first. She'd be polite but also a bit cautious, as she doesn't know what this Saiyan from Goku's past might be like. But as she sees Goku's joy, she'd warm up to Bardock.
Chi - Chi might also be heartbroken. She loves Goku deeply despite his flaws. In fanfiction, she may initially be in denial, thinking that Goku will come back soon. But as time passes, she realizes that he may not return, and this could lead to a deep sense of sadness and loneliness. She has to then figure out how to raise their children on her own.
There could be various fanfictions. Maybe some that focus on alternative endings, like ones where certain characters survive who didn't in the original. For example, a fanfiction where Erwin survives and leads the Scouts in a different way.
It could mean that a person who is a fan of 'Attack on Titan' (AOT) is reading or watching fan - created fictional works related to AOT. Maybe they are interested in seeing different interpretations or storylines that fans have come up with.