Sasuke would probably be very confused at first. He has spent so much time hating Itachi for what he did to the Uchiha clan. Seeing Naruto befriend Itachi would make him question his own long - held beliefs. He might initially be angry with Naruto for seemingly siding with his enemy.
Sakura's reaction would be complex. She has deep - seated feelings for Sasuke, so it would be a hard pill to swallow. However, as a medical ninja, she would also feel a sense of responsibility towards Sasuke's pregnancy. She might offer to be Sasuke's doctor throughout the pregnancy. Naruto's friends like Rock Lee would be over the moon for him. Lee would see it as Naruto achieving another great milestone in his life. He would constantly cheer them on and might even start training extra hard in case he needs to protect the new family. As for the other Konoha ninjas, they would initially be skeptical but gradually accept the situation as they see Naruto and Sasuke's determination to build a family together.
He'd probably be very intrigued. Percy has a penchant for adventure and new things, and this fanfiction would be something completely different from what he's used to.
I think young Sasuke would have a very intense reaction. He was so consumed by his hatred for Itachi at that young age. A Sasuke vs Itachi fanfiction would be like a trigger for him. He would be eager to see how the fictional fight is portrayed. If Sasuke in the fanfiction is shown as strong, it might fuel his own ego and make him strive even harder to become powerful. However, if the fanfiction shows Itachi as superior, it could enrage him. He might feel that it undermines his own goal of defeating Itachi and he might even want to find the writer to correct their 'wrong' view.
Boruto's reaction would be complex. He'd be heartbroken, for sure. He might start to question his own worth and purpose. But over time, he'd realize that he has to carry on Naruto's legacy. He'd become more serious and focused. He'd also become more empathetic towards others, understanding the weight of sacrifice. He might even start to study Naruto's techniques and leadership style more closely, trying to emulate the things that made Naruto such a great Hokage and hero.
As of now, Naruto and Sasuke haven't died in the Boruto manga. Their characters continue to play significant roles and contribute to the story's development.
Sakura would probably be a bit shocked at first but then be very supportive. She has always cared about both Naruto and Sasuke, so she would likely be there to help with the baby's medical needs if any. Kakashi would be the cool uncle type. He'd offer his wisdom and maybe some training tips for when the baby grows up.