In fanfiction, when Shanks meets Luffy's crew, it could be a very emotional reunion. Shanks might be impressed by how much Luffy and his crew have grown. He could see the strong bonds within the crew and be proud of Luffy for leading them so well.
Well, it's possible that Mang gets back together. But we need to know more details about the situation, like the reason for the initial split and the efforts made by both parties since then.
The story of a broken mirror being reunited usually referred to the story of two people who broke up for some reason but met again under some chance or coincidence and got back together. This kind of novel usually involved the emotional entanglement between two people and the various challenges and difficulties they faced after they got back together. Some novels would also describe the conflicts and misunderstandings between the two and how they would resolve these estrangement after they got back together.
If Luffy kisses Nami, it could cause a stir among the crew. Sanji might be extremely jealous as he has his own feelings for Nami. Zoro, on the other hand, would probably make sarcastic remarks about it. But overall, it could also bring the crew closer as they see Luffy and Nami in a new light and start to think more about relationships within the group.
Shanks might interact with Luffy's crew in a very friendly and father - like way. He could pat the crew members on the back, give them words of encouragement, and share his experiences with them.