)
During the year following a parent’s death, the children should increase their Torah study, mitzva observance, and good deeds. The more they do so, the more helpful they are in saving their parent’s soul from hell and elevating it in heaven. This applies even if the parent was righteous and certainly needs no help to merit reward in the afterlife. The soul enjoys and is elevated by the good deeds the children undertake in their parent's memory. It certainly applies if the parent was not righteous.
A son in mourning is required to say Kaddish in synagogue daily to elevate his parent’s soul. If the son knows how to lead the weekday services and the congregation is agreeable, it is preferable for him to do so. It is customary to say Kaddish for only eleven months, stopping either a month or a week short of the full twelve months. This is because there is a tradition that the wicked spends a year in hell. If the son said Kaddish for the entire twelve months, it might imply that he thinks his parent was wicked. Kaddish is recited for the full year only if the deceased is halakhically considered wicked, such as someone who converted to another religion or someone who committed suicide (not due to mental health issues).
Even a son who is under the age of bar mitzva says Kaddish for his parents. What if there is no son to say Kaddish? If the deceased has a God-fearing father, grandson, or son-in-law, that relative may say Kaddish for him. If no male relative is available to recite Kaddish, the family should take money from the estate to hire a God-fearing person to say Kaddish.
An adopted child needs to say Kaddish for his adopted parents. It is proper for a convert to say Kaddish for his non-Jewish parents.
