Should he arrange his children’s marriages or do Hajj with the money that he has?

Firstly:

Hajj is
obligatory and must be done immediately by the one who is able to do it and
who meets all the conditions of it being obligatory, and it is not
permissible for him to delay it without an excuse. For more information,
please see the answer to question no. 41702.

Secondly:

It is obligatory
for a man to arrange the marriage of his son, if the son needs to get
married and cannot afford the expenses thereof. This is included under the
heading of obligatory spending according to the Hanbalis.

Ibn Qudaamah
(may Allah have mercy on him) said in al-Mughni (8/217):

Our companions –
i.e., the Hanbalis – said: It is the father’s duty to keep his son chaste,
if he is responsible for spending on his maintenance and he needs that which
will keep him chaste. End quote.

Al-Mirdaawi (may
Allah have mercy on him) said in al-Insaaf (9/404):

it is obligatory
for a man to keep chaste those on whom he is obliged to spend, including
parents, grandparents, children, grandchildren and so on, among those for
whose  maintenance he is responsible. This is the correct view according to
our madhhab (i.e., the madhhab of Imam Ahmad). End quote.

Shaykh Ibn
‘Uthaymeen (may Allah have mercy on him) said:

A person’s need
for marriage is a serious matter, and in some cases it may be like his need
for food and drink. Therefore the scholars said that it is obligatory for
the one who is obliged to spend on a person to arrange his marriage, if he
can afford that. So it is obligatory for a father to arrange the marriage of
his son, if the son needs to get married and does not have sufficient wealth
to get married. End quote from Majmoo‘ Fataawa Ibn ‘Uthaymeen (18/410).

Thirdly:

The excuses that
make it permissible to delay Hajj include a man arranging the marriage of
his son, if the latter needs to get married and he fears that he may fall
into temptation and that which is prohibited, and his wealth is sufficient
either to do Hajj or arrange his son’s marriage. Hajj is not obligatory for
a man unless he owns wealth surplus to what he needs for his own maintenance
and that of those on whom he is obliged to spend, and arranging the marriage
of his son comes under the heading of obligatory spending, as mentioned
above. Moreover, for a man to keep his son chaste and protect him from
falling into that which is prohibited, at times when temptations and desires
are powerful, is something that cannot be delayed, whereas it is possible to
delay Hajj until after the son’s marriage has been arranged.

Ibn Qudaamah
(may Allah have mercy on him) said in al-Mughni (3/217):

It is essential
that this (i.e., the money for Hajj and the expenses thereof) be surplus to
what he needs to spend on his dependents for whose maintenance he is
responsible, during his trip until he returns, because maintenance has to do
with people’s rights, and their need is greater and their rights are more
affirmed.

If he needs to
get married and fears that he may fall into that which is prohibited, then
he should give precedence to getting married, i.e., he should give it
precedence over Hajj, because that is obligatory for him and he cannot do
without it, so it is like spending on his maintenance.

But if he does
not fear that, then he should give precedence to Hajj, because marriage is
voluntary and should not be given precedence over the obligatory Hajj. End
quote.

And he (may
Allah have mercy on him) also said – as noted above – Our companions said:
The father is obliged to keep his son chaste if he is responsible for his
maintenance and he needs to keep his son chaste.

End quote from
al-Mughni (8/217).

His Excellency
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him) was asked:

I am a young
man, eighteen years old, and am in high school. My mother is approximately
fifty-eight years old, and my father died fifteen years ago. My mother wants
to go for Hajj, but she says: That is not permissible and is haraam until I
get married. I hope that you could advise me as to whether my mother should
give precedence to arranging my marriage before she does Hajj.

He replied:

Undoubtedly Hajj
is obligatory upon everyone who has the means to do it, because Allah, may
He be glorified and exalted, says (interpretation of the meaning):

“And
Hajj (pilgrimage to Makkah) to the House (Ka‘bah) is a duty that mankind
owes to Allah, those who can afford the expenses (for one’s conveyance,
provision and residence)”

[Aal ‘Imraan
3:97].

So if you have
the means to do Hajj in terms of finances, then it is obligatory upon you,
and if she has the means to do Hajj in terms of finances, then Hajj is
obligatory. But if you start with marriage, because you need to get married,
then there is nothing wrong with that, because marriage is also obligatory
when one has the desire and wish for it, because the Prophet (blessings and
peace of Allah be upon him) said: “O young men, whoever among you is able
to, let him get married. Whoever is not able to, he must fast, for it will
be a shield for him.” Whatever the case, there is nothing wrong with giving
precedence to Hajj over getting married.

End quote from
Fataawa Noor ‘ala ad-Darb by Ibn Baaz (20/42).

If the situation
is as the questioner mentioned in his question, that he fears temptation for
his children and wants to arrange the marriages of some of them with the
wealth with which he would otherwise do Hajj, then in this case there is
nothing wrong with him delaying Hajj until Allah makes it easy for him, so
as to ward off this great evil.

And Allah knows
best.