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

Qurbani = Sacrifices, - My wife and I live with my father; is one
sacrifice sufficient on behalf of all of us, or do we have to offer
two sacrifices?.
Praise be to Allaah.
One sacrifice is sufficienton 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
ofAllaah (peace and blessings of Allaah be upon him)? He said: A man
would offer a sheepon 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.