Is it better to repeat Hajj for himself or to do Hajj on behalf of his relatives?

It is better for him to do Hajj on his own behalf, because
this is the basic principle, and he can make du’aa’ for himself and for
others among his relatives and all the Muslims. But if one or both of his
parents did not do the obligatory Hajj, then he may do Hajj on their behalf
after doing Hajj for himself, as a way of honouring them and treating them
kindly when they are incapacitated or after they have died. But he should do
Hajj or ‘Umrah for each of them separately; he cannot combine them both in
one ‘Umrah or one Hajj. End quote. 

Fataawa al-Lajnah al-Daa’imah,
11/66 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was
asked: A woman wanted to do Hajj on behalf of her mother who had died, but
her mother had done the obligatory Hajj. Which is better: to do Hajj on her
behalf or to make du’aa’ for her? 

He replied: 

It is better for her to do Hajj for herself, and to make
du’aa’ for her mother, because the Prophet (peace and blessings of
Allaah be upon him) said: “When a man dies, all his good deeds come to an
end except three: ongoing charity (sadaqah jaariyah), beneficial knowledge,
or a righteous son who will make du’aa’ for him.” He did not say: a
righteous son who will do Hajj on his behalf or fast on his behalf or give
charity on his behalf or pray on his behalf. If someone were to ask us:
which is better, to pray and give the reward to my father, or to give
charity and give the reward to my father, or to make du’aa’ for my father?
We would say: it is better to make du’aa’ for your father, because the
Messenger (peace and blessings of Allaah be upon him) knew more than
us, and was more sincere than us, and more eloquent than us, and he did not
say, a righteous son who will do good deeds on his behalf; rather he said: a
righteous son who will make du’aa’ for him. This is what the Prophet
(peace and blessings of Allaah be upon him) taught us. End quote. 

Fataawa Ibn ‘Uthaymeen, 21/251.