I have Ozzie sleeping in his main cage, I do have anther cage that is made for cockatiel that is avaliable (it is big enough for two alexandrine) but Ozzie can easily chew through that cage so I just leave him in his main cage.
However, having two cages will help with territorial aggression. But Ozzie is not on his cage about 60-80% of the day anyway. He is only in his cage when no one is home and at night, most of the time he is either with someone is the house or is on his play stand. If Poe have sign of cage aggression, then a second cage is ideal.