What is the appropriate amount for the aqiqah for a boy and a girl, and is it better to give money or to share in a cow, and is performing it in Ramadan better?

The 'aqiqah (definition) is a confirmed Sunnah (definition), and it can be slaughtered whenever it is easy to do so. Charity in Ramadan (definition) is better. The Sunnah is to sacrifice two sheep for a male and one sheep for a female. The Shafi'is have permitted sacrificing for the newborn with the amount that suffices for an udhiyah (definition) (sacrificial animal), but it is better to sacrifice two sheep for a boy and one sheep for a girl. Giving money as charity instead of slaughtering the 'aqiqah is not sufficient.