models.py:

class Editorial(models.Model)
    ...

class Group(models.Model):
    editorial = models.ForeignKey(Editorial)

class Link(models.Model):
    group = models.ForeignKey(Group)

forms.py:

from nested_formsets.formsets import NestedInlineFormSet
from nested_formsets.forms import NestedModelForm

class GroupInlineFormSet(NestedInlineFormSet, BaseModelFormSet):
    pass

class GroupForm(NestedModelForm, forms.ModelForm):
    nested_formset_class = inlineformset_factory(Group, Link)
    class Meta:
        model = Group

admin.py:

class GroupLinkInline(StackedInline):
    model = Group
    form = GroupForm
    formset = GroupInlineFormSet

class EditorialAdmin(admin.ModelAdmin):
    inlines = (GroupInline,)

overload admin/edit_inline/fieldset_inline.html and add the code below before the close fieldset tag

{{ fieldset.form.get_nested_formset.as_p }}