Slaughtering for the deceased after burial is an act of Bid`ah (innovation in religion) for which there is no evidence in the Qur'an and the Sunnah. Taking the price of the slaughtered sheep from the property of the deceased is doing injustice to the heirs and is an unjust consumption of people's money. Its reward will not be credited to the deceased as it is unlawful, and its price is unlawful too.
According to evidence, what benefits the deceased is making Du`a' (supplication), giving Sadaqah (voluntary charity), and performing Hajj or `Umrah on their behalf.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.