After a son is finished saying Kaddish for the eleven months, during the twelfth month before the yahrtzeit, is it preferable to volunteer to be the baal tefillah if there is no one else who is saying Kaddish in the minyan who is willing to be the baal tefillah or no one else there who is saying Kaddish? Thank you!

Shalom, Thank you for your question. It is permitted to be the chazan even in the 12th month when kaddish is not said, however it is not an obligation. Some are of the opinion that it is good to be the chazan (Igros Moshe, Y.D. 4:61-17. See also Shevet ha-Levi 2:161.) See, however, Chut Shani, Ribbis, pg. 172, where Rav N. Karelitz recommends that a mourner should not serve as sheliach tzibbur during the twelfth month. [from an article by Rabbi Doniel Neustadt online]. In any event he has no priority over any other person. Blessings.