All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
We ask Allah to help you in this great mission of the Prophets to make clear to the people the true religion, calling them to it and warning them against polytheism by informing them of its bad consequences.
We advise you to be kind and polite when calling your family members to true Islam. While calling them, offer them gifts and be good to them as this might make your speech acceptable and might have a good impact on them. The Daa'iyah (the one who calls people to Islam) should be a good opportunist and whenever people are afflicted by accidents, crisis and illnesses, he should remind them that it is only Allah who removes their worries and answers their Du'aa’ (supplications). It is He Who cures the sick and satisfies the needs of the people. Only Allah can provide these benefits.
Emphasize the weakness of the creatures, their dire need to Allah no matter their strength, health, wealth or piety. If, for instance this Wali (pious person) were able to help himself, he would have raised himself from the grave and cleaned his body from the dust.
Every Muslim knows that the most outstanding of the pious people are the companions of the Prophet like Abu Bakr, ‘Umar, ‘Uthman and ‘Ali . If taking intermediaries were from the religion, then these four Caliphs would have been the most deserving to be put in this position and not these later people who cannot be compared to these righteous companions of the Prophet .
It is not proved that anybody during the time of the companions or their followers came to the graves of ‘Umar or Abu Bakr and sought their help or gave them vows.
Ask help from Allah and seek refuge with Him. Indeed, the keys of the hearts are with Him. Do not become pessimistic. Repeat your advice many, many times and we hope that Allah will guide them to the right path through your efforts.
Allah knows best.