class ProjectGroupMembershipInlineForm(forms.ModelForm):

    def __init__(self, *args, **kwargs):
        super(ProjectGroupMembershipInlineForm, self).__init__(*args, **kwargs)
self.fields['group'].queryset = Group.objects.filter(some_filtering_here=
    self.instance)
Администратор django встраивает: получить объект из formfield_for_foreignkey