title: Django admin - property options based on a related parent model
body: <p>I have a parent and a child class. The relation between them is many-to-one like this:</p>
  <pre><code>class Parent(AccessmanagerMixin, models.Model):
      name = models.CharField(max_length=150)
      def __str__(self) -&gt; str:
          return self.name
  
  class Child(AccessmanagerMixin, models.Model):
      name = models.CharField(max_length=150)
      parent_group = models.ForeignKey(Parent, on_delete=models.CASCADE,  null=True )
      def __str__(self) -&gt; str:
          return self.name
  </code></pre>
  <p>they both have a many-to-many relation with the User class, named read_users (its a custom security on object level).</p>
  <pre><code>class AccessmanagerMixin(models.Model):
      read_users = models.ManyToManyField(User, related_name='read_users')
      class Meta:
          abstract = True
  </code></pre>
  <p>For example in the admin I would like to use the users from Parent read_users as an option for selecting the read_users for the Child entity? How can I do this in a best way?  Can I
  override the read_users property in the Child admin.ModelAdmin.</p>