Can a paish-namaz (leader of congregational prayers) lead the jamaat (congregation) of Eid prayers twice?
A paish-namaz who has led Eid namaz once at a place, cannot lead Eid namaz again that day.
Same is the ruling for jamaat of jumah (Friday) namaz and daily namaz.
Is it permissible for a woman to lead the congregation (jamaat) in which men are also following her?
A woman can lead other women in congregational prayers, but it is not permissible for a man to offer his prayers in a woman-led congregation.
Please clarify that can we pray our prayers behind the Sunni Imam.
To promote Islamic Brotherhood one may offer his namaz behind a Sunni leader of congregational prayers provided that he says his own azan and iqamat, and has the niyyat (intention) of furada (single) namaz.