I (both Ty Lee and Mai are played by me, I couldn't wait for a Mai to be applied for so I just apped her in the end) treated Azula as if she was the same person but had forgotten. Ty Lee (the character) was confused under the circumstances but didn't question it, it's not in her nature to question what Azula says so she just went with it. And Mai was too shocked at being ordered to return to say anything and played dumb.

It depends, with my situation the three were apart for some time due to plot so something happening to one that made them forget the comm wasn't farfetched. If another Phoenix is applied for, maybe it could be one from another dimension of some kind or a virus hit him that made him forget the community (but not his interactions with the people that he'd interact with normally, I've never played the games but, y'know).