Djangoのuserクラスの拡張について

AUTH_USER_MODEL = 'A.User'
AUTH_USER_MODEL = 'B.User2'

#models.py
#Aフォルダ
class UserManager(BaseUserManager):
    use_in_migrations = True

    def _create_user(self, email, password, **extra_fields):
        email = self.normalize_email(email)
        user = self.model(email=email, **extra_fields)
        user.set_password(password)
        user.save(using=self._db)
        return user

    def create_user(self, email, password=None, **extra_fields):
        extra_fields.setdefault('is_staff', True)
        extra_fields.setdefault('is_superuser', False)
        return self._create_user(email, password, **extra_fields)

    def create_superuser(self, email, password, **extra_fields):
        extra_fields.setdefault('is_staff', True)
        extra_fields.setdefault('is_superuser', True)

        if extra_fields.get('is_staff') is not True:
            raise ValueError('Superuser must have is_staff=True.')
        if extra_fields.get('is_superuser') is not True:
            raise ValueError('Superuser must have is_superuser=True.')

        return self._create_user(email, password, **extra_fields)

class User(AbstractBaseUser, PermissionsMixin):
    uuid = models.UUIDField(default=uuid.uuid4, primary_key=True, editable=False)
    username_validator = UnicodeUsernameValidator()

    username = models.CharField(
        _('username'),
        max_length=150,
        blank=True,
        null=True,
        help_text=_('Required. 150 characters or fewer. Letters, digits and @/./+/-/_ only.'),
        validators=[username_validator],
        error_messages={
            'unique': _("A user with that username already exists."),
        },
    )
    email = models.EmailField(_('メールアドレス'), unique=True,null=True)

    is_staff = models.BooleanField(
        _('staff status'),
        default=True,
        help_text=_('Designates whether the user can log into this admin site.'),
    )

    is_active = models.BooleanField(
        _('active'),
        default=True,
        help_text=_(
            'Designates whether this user should be treated as active. '
            'Unselect this instead of deleting accounts.'
        ),
    )

    objects = UserManager()

    USERNAME_FIELD = 'email'
    REQUIRED_FIELDS = []

    class Meta:
        db_table = 'User'
        verbose_name = _('user')
        verbose_name_plural = _('ユーザー')

    def clean(self):
        super().clean()
        self.email = self.__class__.objects.normalize_email(self.email)

    def email_user(self, subject, message, from_email=None, **kwargs):
        send_mail(subject, message, from_email, [self.email], **kwargs)

    def get_uuid(self):
        return self.uuid

   #models.py
   #Bフォルダ
   #上記と殆ど同じため割愛
   class Meta:
        db_table = 'User2'
        verbose_name = _('user')
        verbose_name_plural = _('ユーザー')