He has two wives; should he offer two sacrifices?

It is sufficient for you to offer one sacrifice. In the
answer to question no. (45916)
we stated that one sacrifice is sufficient for a man and the members of his
family even if they are one hundred strong, and the Prophet (peace and
blessings of Allaah be upon him) used to offer a single sheep on behalf of
himself and his family, and when he (peace and blessings of Allaah be
upon him) died he left behind nine wives. 

Al-Qurtubi said: 

There is no report that the Prophet (peace and blessings
of Allaah be upon him) ordered each of his wives to offer a separate
sacrifice, even though the sacrifice was repeated every year and his wives
were numerous. This would have been narrated if it has happened, as other
minor issues were narrated. This is supported by the report narrated by
Maalik, Ibn Maajah and al-Tirmidhi, who classed it as saheeh via ‘Ata’ ibn
Yasaar: 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.” End quote from
Fath al-Baari. The hadeeth was classed as saheeh by al-Albaani in
Saheeh al-Tirmidhi. 

Al-Bukhaari (7210) narrated from ‘Abd-Allaah ibn Hishaam (may
Allaah be pleased with him), that he met the Prophet (peace and
blessings of Allaah be upon him) when his mother Zaynab bint Humayd took him
to the Messenger of Allaah (peace and blessings of Allaah be upon him),
and said: “O Messenger of Allaah, accept his oath of allegiance.” The
Prophet (peace and blessings of Allaah be upon him) said, “He is too
young.” He patted him on the head and made du’aa’ for him, and he used to
sacrifice a single sheep on behalf of his whole family. 

Al-Haafiz said: The phrase “and he used to sacrifice a single
sheep on behalf of his whole family” refers to ‘Abd-Allaah ibn Hishaam. End
quote. 

The Standing Committee was asked: 

I have two households which are about fifteen kilometers
apart, and I want to offer the sacrifice. Should I offer a sacrifice at each
house, or at one house? 

They replied: 

It is sufficient for you
to offer one sacrifice on behalf of your two households, so long as the head
of both is one person. But if you offer a separate sacrifice at each house,
that is better. End quote. 

Fataawa al-Lajnah al-Daa’imah,
11/407.