Is it permissible to perform the Hajj on behalf of a deceased grandfather who did not pray and died while not praying, and is it permissible to supplicate for his forgiveness and give charity on his behalf or do good deeds for him?

If the grandfather died denying the obligation of prayer, then he died as a disbeliever. It is not permissible to supplicate for him or seek forgiveness for him, as Allah the Almighty says: (And Abraham’s prayer for his father’s forgiveness was only because of a promise he had made to him. But when it became clear to him that he was an enemy of Allah, he disassociated himself from him.) However, if he died abandoning prayer while affirming its obligation, the preponderant view is that he is also a disbeliever. Yet, some scholars hold that he is not a disbeliever in this case, and therefore it is permissible to supplicate for him, perform Hajj, and give charity on his behalf.