Mourning Close Relatives During A Parent’s shiva
A man was sitting shiva for his father. During the shiva he was informed that his paternal aunt had just passed away and that she has no one to say kaddish for her apart from him. Is he now permitted to attend his aunt’s burial in order to say kaddish?
From the third day of shiva and on, he may attend a funeral of a relative, and return home immediately afterwards.
If there will be no minyan or no one to say kaddish at the burial, he may attend even from the first day.
שלחן ערוך יורה דעה שצג סעיף ב, גשר החיים פרק כא יג – יד