class Element(models.Model):
     Source1 = models.ManyToManyField(Source1)
     Source2 = models.ManyToManyField(Source2)
     Source3 = models.ManyToManyField(Source3)


Ranked = (Link.objects.all().aggregate(
         Ranked=Sum(F('Source1') + F('Source2') + F('Source3'), output_field=IntegerField)['Ranked']
))