I'm not sure how it works for those two, but...with Sora and I? We're connected. I can see all of his memories and he gets a few glimpses of mine. Or did. It hasn't happened since we've been here. But beyond that, Sora and I were able to function separately for a long time, almost a year. [But that's leaving out everything that happened during his year with the Organization including the flood of memories and the comas and the killing of his best friend who was an imperfect replica, but, you know, details.]

Back home though I had to merge with Sora so that he could continue fighting the darkness. He was only at about half his strength without me there.