If someone has only one living parent and they are asked on behalf of someone else to say kaddish for a deceased family member on their yahrtzeit is there any makom in halacha or minhag (aside from perhaps personal feelings) to not say kaddish for someone on their yahrtzeit? Better to find someone who’s both parents are already nifter to say kaddish?
Answer:
Based on the Maharil, the Rema (132:2) writes that if a parent is makpid, one should not say kaddish. This halachah refers to one parent. As the Levush (133) writes, there is no halachic problem of saying kaddish, and this depends only on the kepeidah of the parent. Therefore, if the parent is makpid, one should not say kaddish, but if the parent is not makpid, one can say kaddish on behalf of a family member.
Note that there is a broad dispute among authorities concerning a father who does not wish his son to say kaddish for his mother. On this question, most authorities rule that the obligation of honoring the mother takes precedence, and the father cannot prevent his son from saying kaddish for her. However, where there is no clash between the honor of respective parents, a child must heed the kepeidah of his parent.
