Identity Quotes in I Know This Much is True

Dominick worries about being confused with Thomas. He doesn't want to be identified as Thomas's brother, much less being identified as Thomas himself. It's like Jerry meeting bizarro Jerry, but not funny.

This is part of the core of Dominick's fear and frustration, and it recalls the quote about twins being one fertilized egg that goes in two different directions. What if the mental illness didn't entirely pack up and go with Thomas? What if it's part of Dominick's identity, too?

This is an exchange between Thomas and Dominick. What do you think Thomas means here? That Dominick is "crazy," too? Or that they're two halves of the same coin? Some sort of clone? What?