ANSWER: This is not from the sunnah. The prophet’s uncle Hamzah and his beloved wife Khadeejah and many others died in his lifetime and he had never slaughtered a sacrifice specially for them.  If you want, you can slaughter your own sacrifice and include in it all the deceased you want. 

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ANSWER: It’s valid as long as they slaughter it within the days of sacrifice (Eid day, 11th, 12th & 13th of Dhul-Hijah)

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