Some of the pirates might be excited to meet Sabo, especially those who knew Ace well. They could see Sabo as a link to their fallen comrade. Others might be more skeptical, fearing that Sabo could bring trouble from the Revolutionaries. Overall, it would be a mix of reactions depending on the individual members of the Whitebeard Pirates.
You can start by searching on fanfic platforms like Archive of Our Own (AO3). Just type in 'ace and sabo' in the search bar, and a whole list of relevant fanfics will pop up.
In fanfiction, their relationships are sometimes explored through shared battles. For instance, they might all fight together against a common enemy, like a powerful navy fleet. During these battles, the trust between Ace, Sabo, Luffy, and the members of Whitebeard's crew is emphasized. The relationships are also shown through quieter moments, like when they are all on the ship sharing stories and dreams, which helps to strengthen the bond between them all.
Their relationship could develop through shared adventures. For example, if they are on a mission to steal important documents from a World Government facility. They would have to rely on each other's skills. Sabo's ability to fight and Koala's knowledge of infiltration. As they face various obstacles, they start to trust each other more deeply, and their relationship evolves from comrades to close friends.
Well, in fanfiction, Luffy's bond with Ace and Sabo is unbreakable. They grew up together and share a lot of memories. When it comes to the Marines, they represent the 'order' that Luffy and his brothers are sort of defying as pirates. Some fanfictions might show a young Marine recruit who has a change of heart after seeing the strong bond between Luffy, Ace, and Sabo. He starts to question whether the Marines are always in the right. Usually, though, the Marines are there to create conflict for the trio.
Luffy, of course. He and Sabo have a deep history. They grew up together and Sabo was like a brother to him. Their reunion would be filled with joy, hugs, and probably a lot of tears. Luffy would be over the moon to have Sabo back in his life and on his ship.
Sabo's done quite a bit. For one, like I said, he's climbed up in the Revolutionary Army. That's no small thing. It shows he's got the skills and the leadership. Then there's the Mera Mera no Mi. Grabbing that devil fruit was huge. It not only gives him power but also kind of ties him to Ace in a way. And in battles against the World Government, he's been standing strong, showing that he's a force to be reckoned with. His actions are all part of his bigger plan to change the world for the better.
Ace's relationship with Whitebeard is already established, but it could grow to be more of a father - son type relationship. Luffy would be in awe of Whitebeard and his crew, and his relationships with everyone would be based on his infectious enthusiasm. Sabo, being the more rational one, would study Whitebeard's leadership style and learn from it. As for the relationship between the three brothers, they would support each other during battles and share their dreams and experiences with the rest of the crew, which would in turn strengthen their bonds with the Whitebeard pirates.
It could shift the power dynamics. Their combined strength would make them a significant force. Enemies might be more cautious or new alliances could form.