class Model1(models.Model):
    model2 = models.ManyToManyField(Model2)
    #...
class Model2(models.Model):
    model3 = models.ForeignKey(Model3)
    #...
class Model3(models.Model):
    custom = models.CharField()

def simple(request, simple_id):
    if request.method == 'POST':
        if request.is_ajax():
            if 'delete' in request.POST:
                id3 = request.POST.get('delete', '')
                Model1.objects.get(id = simple_id).model2.filter(model3__id = id3).delete()

<form action="" method="post" id="simple">{% csrf_token %}
<input type="submit" name="delete" id="simple_delete" value="">
</form>

$('.deletebutton').click(function(){
    id = $(this).attr('data-id');
    $('#simple_delete').attr('value', id);
    $('#simple').ajaxForm();
    $('#simple_delete').click();
});