He is not part of the family.
I knew it. I knew I was right to keep being cautious about claims of Spider's adoption, no matter if it was Empire Magazine writers calling Spider "Jake's adopted son" or if it was people on the internet saying Jake saying "son for a son" = adoption. I knew that was too simple. No actual proof of adoption, just vibes. After A2 promos lying about it I just couldn't believe it without evidence. And I was right. Here comes confirmation straight from Cameron's mouth (from production notes):
I knew it. Neytiri didn't agree to it. Spider didn't wear the white stripe. And they were going to just ship him to High Camp all alone. "He is not part of the family."
It might be "not yet" but for now this is where we are.
No wonder Quaritch, who is a horrible person but likes Spider just the way he is, doesn't try to change him and shows he cares about Spider more than his goals, makes Spider feel conflicted. It sucks when the only person who accepts you is abhorrent in every other way.
Spoilers from leaked script pages under the cut.


















