Dear Rabbi Simon,
I was wondering how a Gentile can respectfully mourn a Jewish loved one? If there are no Jewish family members who are able to lead the mourning, how can a Gentile make sure that the deceased is respected and properly mourned according to Jewish customs?
TY for your sensitive question. Depending on the details of the circumstance to which you refer, there may be a number of possibilities, but the most accessible and widely applicable would be to seek to insure that the kaddish memorial prayer is recited on behalf of the Jewish deceased. This well-known ancient prayer is recited as an act of respect for one who has passed from this world. Where the deceased has no living progeny (or even if s/he does) the prayer may be recited by another Jew.
There are charitable organisations who will undertake (no tasteless pun intended) this mitzvah on behalf of any deceased Jew, upon offering a donation to support their work. An example of this would be https://www.hebrewfreeburial.org/what-we-do/kaddish-services/.
The prayer can be recited daily for a year, or other intervals. Contact them for more information.
May we only hear of good news in the future.
Rabbi Rashi Simon