Is what the father is experiencing in terms of harassment a trial from Allah due to his shortcomings in helping orphans and the needy among his relatives, and what is your advice to him?

Charity repels affliction from the giver, and it is among the good deeds that protect against evil ends, as the Prophet, peace and blessings be upon him, said: "Good deeds protect against evil ends, secret charity extinguishes the Lord's wrath, and maintaining kinship ties increases life." Also, he, peace and blessings be upon him, said: "Good deeds protect against evil ends, calamities, and destructions, and the people of good deeds in this world are the people of good deeds in the Hereafter."

A grandfather's expenditure on his deceased son's children is both charity and a act of kinship, whether it is obligatory upon him or not.