One sacrifice is sufficient on behalf of all the members of a household

One sacrifice is
sufficient on behalf of all of you, because it is narrated in the Sunnah
that one sacrifice is sufficient on behalf of a man and the members of his
household. 

Al-Tirmidhi
(1505) narrated that ‘Ata’ ibn Yasaar said: I asked Abu Ayyoob: How was the
sacrifice done at the time of the Messenger of Allaah (peace and
blessings of Allaah be upon him)? He said: A man would offer a sheep on
behalf of himself and the members of his family, and they would eat some and
feed others with some.” Classed as saheeh by al-Albaani in Saheeh
al-Tirmidhi. 

The Standing Committee was asked: 

If my wife lives in the
same house as my father, is it sufficient for me to offer one sacrifice on
Eid al-Adha on behalf of myself and my family, or not?

 They replied: 

If the situation is as
you describe, with a father and son living in the same house, it is
sufficient to offer one sacrifice on behalf of yourself, your father, your
wife, your father’s wife and all the members of your household, in
accordance with the Sunnah.” End quote.

 Fataawa al-Lajnah al-Daa’imah,
11/404.