Isaac has always been quiet and serious, as far as I know. It's different for us, obviously, we haven't been together our entire lives the way you guys have, but he was like that when we met anyway and his powers seemed to [...] not exaggerate it exactly, but it's like they went hand in hand almost? I don't know if that makes sense.
Everyone's different though. I think your sister was just always going to be a kind of opposite to you even without powers, you know?