A Muslim may not ask for the forgiveness or Paradise of someone who died upon disbelief or shirk: "It is not for the Prophet and those who believe to ask forgiveness for the polytheists, even if they be near relatives, after it has become clear to them that they are the companions of Hellfire" (Quran 9:113). Abu Hurayrah narrated that the Prophet (peace be upon him) visited his mother's grave and wept, and said, "I asked my Lord's permission to seek forgiveness for her and He did not permit me, and I asked His permission to visit her grave and He permitted me — so visit graves, for they remind you of death" (Sahih Muslim 976). So visiting the grave as a reminder of death is allowed, while supplicating for their forgiveness is not, and salat al-janazah is not offered over them. Many scholars also allowed a Muslim to accompany the body and take part in burying a non-Muslim relative, without participating in the religious rites of another faith. What remains open to you is a great deal: kindness and patience with the family, offering condolences, helping with practical arrangements, and speaking well of the good they did, since Allah does not forbid you from dealing kindly and justly with those who did not fight you over religion (Quran 60:8). Direct your grief into duʿa for yourself and the living, and leave their affair to the Most Merciful of those who show mercy.
Q&A · Death & Afterlife
Can I pray for a non-Muslim parent or relative who has died, or attend their funeral?
Evidence — the daleel
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.