It could be that 8 people survived the plane crash (in their made up story) and then 2 of them later died on the island by sickness or accident or of their crash related injuries. That would make their story of survival more believable. I think they are passing Aaron off as Kate's biological child, time difference or not, she's been on the run for years so she could've had a child that the authorities didn't know about...then again you'd think the marshall would've told someone, unless he hadn't contacted anyone about the capture yet. Kate's mom really wanted to see her grandchild, not sure she'd be so determined if she knew he wasn't her biological grandchild? Especially since she's been so cold to Kate. The idea of Michael and Walt being the other 2 makes sense also. Except would Jack include that in his story? Why wouldn't Michael and Walt be part of the group then and be the Oceanic Eight?