My wife converted shortly after high school, before I knew her. Her family was very supportive (if not completely understanding) at that time, some 30 years ago, and until the present time. We are Torah observant, shomer mitzvot, and active in our large orthodox community. Because our relationship with her family has always been mutually warm, respectful and involved, while maintaining our distinct identity and requirements, we have worked very hard to anticipate and prepare for foreseeable events. At present, her parents are elderly and in poor health. I am thinking about how to properly observe the death of parents that are not Jewish. We have already gone through Avelut for each of my parents, and my wife and my children were extremely supportive, as well as my wonderful community. But this would be a very different situation. One does not observe the halachot or minhagim for a non-Jew. On the other hand, her parents are very special people and we love them. When they die, we will feel as much of a loss, and feel the pain, and feel like mourning just as if they were Jewish. Our community, also, will want to express condolences to my wife, to our family, and even to her family (who they also know). But we would not be observing Shiva; no one would be saying Kaddish; no Shloshim; no Matzevah. How should an observant Jew properly respond at the time of death of a non-Jewish parent? During the period immediately following the death? During the year following the death? On the anniversary of the death? How should the Jewish friends and the Jewish family members express their concern, both to the Jewish mourner, and to the non-Jewish survivors?
The Halachot of mourning (sitting in low chair, torn garment etc.) should not be observed. However, it is proper to set aside a time to accept condolences, and learn Torah in the memory of a non-Jew. One may give charity in their honor and according to some authorities recite kaddish. An orthodox Jew may participate in the funeral of a gentile as long as there is no mass. The anniversary of death may be marked in above mentioned ways.