[Answered ]-Django multiple user with multiple groups problem at signup

This issue is caused because the signal sender is the User model itself. So saving the user instance of one of the profiles will call both the professeur_profil and etudiant_profil receivers. One approach to fix this is to change the senders of the receivers to the profile model instead:

@receiver(post_save, sender=Professeur)
def professeur_profil(sender, instance, created, **kwargs):
    if created:
        group = Group.objects.get(name='prof')
        instance.user.groups.add(group)


@receiver(post_save, sender=Etudiant)
def etudiant_profil(sender, instance, created, **kwargs):
    if created:
        group = Group.objects.get(name='etudiant')
        instance.user.groups.add(group)