Well, in such a fanfic, Sarada might summon the Hokages to seek their advice on how to deal with a powerful enemy threatening the village. For example, she could ask Hashirama about his experience in founding Konoha and how to protect it from the roots.
Sarada might be initially shocked and sad. She loves both her parents, and the divorce would be a huge blow to her. She could become withdrawn for a while, not wanting to talk to her friends about it.
Itachi would probably be very calm and composed. He might see Sarada as a symbol of the new generation of ninjas in the village. He could be gentle with her, perhaps sensing her potential and her desire to grow as a ninja.
Naruto would probably be extremely happy and excited. He has always been close to Sakura, and seeing her become a mother would be a big moment for him. He might be there to support her during the birth, bringing some of his positive energy to the situation.
The ninja world would likely be filled with a mix of reactions. Some would see it as a positive sign of unity between different clans. Others might be worried about the power the baby could potentially have. There could be those who would try to use the baby for their own political or power - hungry motives.
Sasuke would likely be initially shocked. He's a man who has been through a lot and is used to a life of solitude and danger. But then, a sense of protectiveness would kick in. He'd become more vigilant about the safety of Sakura and their unborn child. He might also start to think about how to be a better father than his own was, in some ways, trying to break the cycle of his family's past.
They might be overjoyed. Since Sarada is part of their family, they would likely welcome her with open arms and big smiles. They could be very proud of how far she has come in her ninja training.
If Naruto were trained by the Hokages in fanfiction, it would be a game - changer. First, his chakra control would improve significantly as they are all masters in that aspect. Second, he'd inherit their wisdom. He might not make some of the stupid mistakes he did in the original story. Third, his reputation would skyrocket even more. People would see him as not just a strong ninja, but one with the blessings and teachings of the greatest Hokages. This would also have an impact on his relationships. His friends might look at him in a different light, with a mix of awe and pride.
In this 'all hokages meet fanfiction', there could be epic battles of different jutsu. Maybe the first Hokage would show his amazing wood - style jutsu to the later generations. And they might discuss how to better protect the Hidden Leaf Village from new threats.