My father died last year on 14th Ellul, and was not buried until 16th Ellul. As this is a leap year, I understand that I stop saying Kaddish in Tammuz after 11 months, but what day is the last - 13th,14th, 15th or 16th? Likewise a similar question about ending the 12 month period of mourning. I understand the Yahrzeit itself will be on 14th Ellul, after 13 months. No problem here, I hope.

The Kaddish is recited for eleven months from burial therefore in your case till the 16th of Tammuz (not inclusive). The twelve months are counted again from the burial as well. The Yahrtzite is on the day of death and in your case the 14th of Elul. (Gesher Hachaim page 329) May Hashem console you among the other mourners of Zion and Yerushalaim.