Offering sacrifices through slaughtering sheep in the shrines of Awliya' (pious people) is still a widespread custom among my family which I have forbidden but they are insisting on practicing. If I say it stands for committing Shirk (associating others with Allah in His Divinity or worship), they say they worship Allah (Exalted be He) properly and they are not sinful for visiting the graves of the Awliya' and for saying in their supplications, "O Allah! By virtue of the status of Your pious servant soandso, cure us or relieve our distress!" I then refute them saying that our religion denies any intermediation between a man and his Lord but they then ask me to leave them alone.
My question is: What is the method you deem fit for reforming them? How should I behave toward them and how should I combat such a Bid`ah (innovation in religion)? Thanks