Tornado of Terror would likely be one of the first to try and take on Evil Saitama. She's powerful and confident, but she would soon realize the extent of his power. Mumen Rider, despite being weak, would still stand up to Evil Saitama out of a sense of justice. He would be quickly defeated but his act of courage might inspire other heroes to step up.
Naruto might initially be heartbroken. He has always longed for his father's love and acceptance, so being disowned would be a huge blow. He could go into a state of depression for a while, withdrawing from his friends and normal activities. But then, Naruto is a fighter. He would likely start to question his father's decision and try to find out the real reason behind it, vowing to prove himself worthy if there was some misunderstanding.
Shikamaru would likely be the voice of reason. He would tell Naruto to think things through clearly and help him come up with strategies for dealing with the new situation. Choji might bring over some food to help Naruto out, as he knows how difficult it can be to take care of a child. Ino would be more interested in the child's appearance and would offer to help Naruto with things like shopping for the child's clothes.
Izuku might be shocked at first. After all, he has grown up without his father. But then he could be filled with a mix of emotions like joy, confusion, and anger all at once.
He might be shocked at first. After all, he has probably only heard stories about his father. Then he could be angry, blaming his father for not being around when he was growing up.
Goku's reaction could be a mix of shock and happiness. On one hand, he never expected to actually meet his parents. On the other hand, he has always longed for a family connection. He might start asking them a million questions right away about their lives, Saiyan culture, and what it was like when he was born.