Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Volume 11, Page 107, Question 12 of Fatwa No.6505
Question: My grandparents [both] from my father and my mother have died and I do not know whether they had fulfilled the[ir] obligation of performing Hajj or not. So is it upon me to entrust someone to perform Hajj on their behalf?
Response: It is legislated for you to entrust someone to perform Hajj on behalf of every single one of them, so long as the one who is to perform Hajj on behalf of every single one of them has [already] previously performed Hajj for himself and that he is noble and trustworthy.
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet ﷺ and his family and his companions.