I think that The scenes with Jack and Kate are before the scene where we saw him freaking out at the airport talking about flying back and forth trying to find the island.
I also think that Jack's dad may very well be Jacob. He was connected with so many of them Jack, Clair (her dad also), he ran into Sawyer and Kate in Australia, and I'm sure there are others.
But now we know why Clair doesn't make it off the island but Aaron does. That still leaves us the sixth one. Kate was "doing something for Sawyer" so he wasn't one of them. It can't be Juliet since she wasn't on the plane. Same for Desmond. I don't think it's Michael because of Walt (where ever he is).
So, that clear?