I found the whole memorial scene implausable. Jack's father has a memorial service, presumably in Los Angeles, and this woman flies halfway around the world just to tell Jack that his father had sired a child in Australia he wasn't aware of.
"Because I thought you needed to know".
Why? Dad's dead. Claire (for as much as anyone knows) is dead. Jack's preparing to move on. Why go through all this effort just to drop this bomb on him (other than the plot line demands it)? And, FWIW, I don't really get why Jack has such a major problem with Aaron's parentage.
Plus, we still don't know who Aaron's father is. That may still be the mystery we learn later.
I'm waiting to see how the Ocenaic Six wind up back together. Currently, Hurley is at the Orchid, Jack is with Sawyer leaving from the helicopter, Kate and Sayid have just been captured by (I think) the Others near the Temple. Sun and Aaron are on the freighter. So, somehow in the finale those six and only those six get rescued and make up the whole set of lies they plan to tell the outside world.