I wonder if some finesse may be required in requesting the transfer in case there is any chance the school would decide to put both twins the less desired classroom.
That was my first thought too. It is the stupid sort of thing schools do. They could go on the theory that twin B is happy because he misses Twin A and Twin A is happy not because the teacher is a better fit bit because Twin A is more mature and Twin B has "social issues". Therefore putting both twins in Twin B's class should be fine.
