Slaughtering (sacrificing) at graves is prohibited, and also the so-called “Jadf”, because of its involving purposes of worshiping and drawing close. The Prophet (peace be upon him) said:
Allah has cursed the one who slaughters (a sacrifice) to other than Allah.
(Part No. 1; Page No. 197) As for the family of the deceased preparing food for those in attendance, this is not the Sunnah; the Sunnah is that they are to have food prepared for them, as it is authentically established that the Prophet (peace be upon him) ordered that food should be prepared for
the family of Ja‘far when he was killed (may Allah be pleased with him).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.