Django - Multiple dependent form

Question

I have extended the Django User model creating a 1-to-1 dependency with the class Profile. There will be many profiles playing in the same Community. And a Profile can be playing in different Communities at the same time. I did this with a Many-to-Many field "members" in the Community Model. This is shown below. (I have reduced the irrelevant code)

class Profile(models.Model):

    user = models.OneToOneField(User, on_delete=models.CASCADE)
    # Extend Users Here 


class Community(models.Model):

    username = models.CharField(max_length=100)
    password = models.CharField(max_length=50) 
    members = models.ManyToManyField(Profile, through='Membership')

    def get_members(self):
        return "\n".join([str(m) for m in self.members.all()])


class Membership(models.Model):

    community = models.ForeignKey(Community, on_delete=models.CASCADE)
    player = models.ForeignKey(Profile, on_delete=models.CASCADE)

When a new profile is created I would like it to be inmediately associated with a Community.
Therefore, in the user registration form I would like to ask him if he wants to join an existing community or create a new one.

I believe I need something as "Multiple Form" but I would appreciate help in what exactly do I need and how I can look for information about it.

Thanks!