admin.py

from django.contrib import admin
from django import forms
from .models import *

class ThroughInline(admin.TabularInline):
    model = Through
    raw_id_fields = ('unter',)
    sortable_field_name = 'order'
    formfield_overrides = {
        models.PositiveIntegerField: { 'widget': forms.HiddenInput }
    }
    autocomplete_lookup_fields = {
        'pk': ('unter',),
    }

class UberAdmin(admin.ModelAdmin):
    inlines = [
        ThroughInline,
    ]

admin.site.register(Uber, UberAdmin)

models.py

from django.db import models

class Uber(models.Model):
    title = models.CharField(max_length=1000)
    unters = models.ManyToManyField('Unter', through='Through', blank=True)

class Unter(models.Model):
    name = models.CharField(max_length=1000)

    @staticmethod
    def autocomplete_search_fields():
        return ('name__icontains',)

class Through(models.Model):
    uber = models.ForeignKey('Uber')
    unter = models.ForeignKey('Unter')
    order = models.PositiveIntegerField()

    class Meta:
        unique_together = (
            ('uber', 'unter'),
        )
        ordering = ('order',)