My father was niftar on 19th Adar last year. I understand that since this year is a leap year, the "12 months" will end on 19th Adar Aleph, even though the Yartzeit is in Adar Bet. I would like to know if this refers to all aspects of mourning or whether there are still certain restrictions which apply until the yartzeit date. Thank you

All the Halachot regarding Avelut (mourning) discuss 'months' and not a 'year' because of the leap year problem. Therefore, all the aspects of mourning will stop when twelve months are up, and the yartzeit will be at the end of thirteen months. No aspects of mourning are kept during the 13th month. Rabbi Ro'i Margalit