162. Yahrtzeit vs. Shloshim
26:5 A person with yahrzeit and a mourner in Shloshim each have priority over those in the year of mourning, though it is appropriate to enable others to say certain Kaddishes. The Kaddish d'Rabbanan and the Kaddish after Aleinu should be given to the yahrzeit or to the one in Shloshim, while other Kaddishes should be given to other mourners if the number of mourners equals the number of Kaddishes.
26:6 A person with yahrzeit and a person in Shloshim each "win some" and "lose some." The one in Shloshim has all the Kaddishes and the yahrtzeit only gets one. But if many people have yahrtzeit, each one gets one even if this leave the person in Shloshim without any. This is because the person in Shloshim has many days in which to say Kaddish but the one with yahrtzeit only has that day.