Can becoming a hafiz let you intercede for disbelieving family?

I heard from a shaykh (on youtube, Bilal Assad) that in a hadeeth it says that like martyrdom, the people who become hafiz (memorize the entire Qur'an) can intercede for their relatives and family members from hell, and some of my family members are not so religious it seems, and my sister might not even be a Muslim at all but Allahu alem (Allah knows best). I do not wish to make takfeer recklessly lest I become a kaafir. But I love my family, and I want them to be in jannah with me, and though I have hostility between me and some of them (except perhaps my sister), I know in jannah all hostility will be removed.