At first blush this dilemma and goodness knows it is a dilemma, looks like a case of weighing one mitzvah (commandment) against another. To wit:
· Doing honor to your mother by respecting her wishes and going to the unveiling
· Observing Yom Kippur
· Saying kaddish for a parent
· Being part of a minion at an unveiling
But everything about the request from your uncle’s family, that you attend the unveiling, is out of whack. Although they seem to be observing a Jewish ritual, an unveiling, they are doing it at a time that no one, but no one, in the Jewish community would approve of. Perhaps they don’t realize how inappropriate it is to try to honor your uncle by doing an unveiling on Yom Kippur. If they are unaware of this, the best thing to do is inform them, politely but firmly, that it is not at all an appropriate time to hold this ceremony, however non-observant your uncle may have been, and they should make other arrangements. Analogies are always a good thing. No church would conduct a funeral on Christmas, Good Friday or Easter Sunday. Unveilings are not done on Yom Kippur.
Oy, if they do know what they are doing and don’t care. It is always inappropriate to ask a person to violate one mitzvah in order to observe another one, especially if the person making the request has control over when the mitzvah is going to occur, and no one’s health is at stake. It’s important to remember that if they are going ahead, even knowing that doing an unveiling on Yom Kippur is no way to honor their family member, that does not obligate you.
No doubt, the toughest part of this would be to go against your mother’s wishes. On a formal level, Jewishly, one does not have to honor a request from a parent that asks you to violate another mitzvah. Jewish tradition acknowledges that there is something to be said for going out of one’s way to honor a parent’s request, and there are a number of midrashim, rabbinic stories, that illustrate this, but they do not invalidate your principled objection. Perhaps presenting her with the reasons why the invitation is so Jewishly inappropriate will persuade her that going to an unveiling on Yom Kippur does not pay honor to your uncle.
I wish you well on trying to navigate your way on this. It is a very challenging situation.