I think only one would become the avatar being two separate persons with separate souls like in that episode where they go to that village with the fortune teller and there are those two twins and one could earthbound and the other couldn't
But who cares about philosophy it's only a cartoon and it's a great idea
Neat concept! I wonder how that would work... one can bend two of the elements, and the other the other two? They can only bend all elements when they are together? They can both bend all? ...This could be lots of fun.