my mother in law passed away in Adar on a normal year, and I say kadish for her on the yahrtzeit. Do I say kadish this year on Adar alef?
Shulchan Aruch (668:7) writes that one should observe the yahrzeit on Adar Sheini, whereas Rema brings that some say it should be observed on Adar Rishon, and adds that some observe both. Mishnah Berurah (668:42) writes that the final opinion is the principle halachah.
You should therefore say kaddish on both Adar months.