Kiddish is a blessing said over Sabbath wine, while Kaddish is said in memory of deceased family members. The word Kaddish itself is not Hebrew but Aramaic, the language of the masses at the time of its origin. Magnified and sanctified be His great name in the world which He created according to His will. May His great name be blessed forever and ever. Jewish law requires sons to recite Kaddish.
Daughters are under no such obligation, but in many Jewish circles they do so.
It is not a prayer that can be recited alone. All the mourners pray in unison, standing and facing Jerusalem. The Talmud explains that reciting Kaddish insures that the memory of the dead will not grow dim. Each year thereafter, at the anniversary of the death, the Kaddish is prayed. When my father voiced his concern, I tried to respond with as much kindness and compassion as possible.