Must I fast sixty days and feed sixty poor people as expiation for striking a six-month-old girl, which led to her death and the death of her mother, and is it permissible to donate the money to an orphanage?

Killing a human by mistake entails two consequences: the Diyah (blood money) payable by the 'Aqilah (male relatives on the father's side), and the Kaffarah (expiation). If the deceased was a single female, the killer owes one Kaffarah and one Diyah. If there were two deceased females, he owes two Kaffarahs and two Diyahs. The Kaffarah is the freeing of a believing slave. If one cannot be found, then it is fasting for two consecutive months. This fasting must not be interrupted by days on which fasting is impermissible, such as Eid and the days of Tashreeq.