"The teaching of the Prophet sallAllaahu 'alayhi wa sallam was that a sheep is sufficient on behalf of a man and the members of his household, even if they are many in number". [Ibn Qayyim rahimahullah (Zaad al-Ma’aad 2/294)]

 
"In fact, a single sheep is sufficient on behalf of the members of a household, even if there are one hundred or more, as is indicated by the Sunnah". [Al-Shawkaani rahimahullah (Nayl al-Awtaar 5/182)]