Yechiel Michel Epstein

“ A mourner is not permitted to leave his house to attend these Slichos prayers, except for the one occurring on the morning of the day before Rosh Hashana, since it has far more extensive prayers. This applies to the day before Yom Kippur as well in places where they have added extensive prayers. A mourner should not act as leader of the congregation’s prayers on the High Holy Days. He should neither act so for twelve months after the passing of his mother or father, except if he is the set prayer leader, or there is no one else who is able to fill that role. ”

“ If one starts to fast these days without any intention regarding the future - if he fasted three times he will need a formal abrogation. If he only fasted twice that would not be necessary, as I have written in the volume on Yoreh Deah, chapter 214 (see there) .
Section 11 There are those who have a custom on the day before Rosh Hashana to eat before first light, to draw a distinction between them and 'Darkei HaEmory' ('the custom of pagan societies') , who had the habit of fasting on the eve of their festivals. ”

“ A prayer leader must intend to fulfill the prayer obligation on behalf of all those who he is representing. If he has an enemy among the congregation, and intents to not include him in the prayers, even those he is close to among the congregation have not fulfilled their prayer obligations. ”