I'm not sure whether or not Claire is dead, but IIRC, according to "fate" she wasn't supposed to raise Aaron in the long run, so it's entirely possible that Kate stole him, or that Claire gave him up. After all, Claire was traveling to the US to give the baby up for adoption. My guess though is that Aaron isn't one of the Oceanic Six. I'm not sure who 5 is, but I'm guessing 6 is Ben.