The truth about Sun and Jin by harvey harvey

Jin & suns parents both knew about the island. They were either born there or know from financial investments with Widmore.

They knew Sun was about to leave Jin, prob knew about her affair, but kept hush in hopes that Jin would land there without sun and all would be forgotton.

Obviously they choose not to discuss it when sun Returns, and not knowing her daughters intentions on going back to find her Husband. She left their daughter behind not telling the truth.

Neither of them are going to be the new jacob. They have a child together, and Joacob would not allow them to abandon that. They were on the island to understand each other better learn about each other a n respect each other. Which they did. That gives them a ticket back to the real world. Once you can accomplish the things you came to the island looking for in your past you are free to leave. They just need to find each other first. They will be the first who can travel on and off the island like Tom.

Their daughter plays no role in this other than to accept each other. Jacob went to their wedding cause he wanted them to live a happy life which he knew they could not without the Island.

Once they have there purpose, they can leave. Its hard to rule out the rest which would be 4 but I think we can.
Jack- father acceptance
Sawyer - Juilette
Sayid - Already taken
Hurley - No purpose

Which makes Hurley the candidate.