He spent on his siblings so that they could get married; can his father allocate something of the estate to him?

Undoubtedly what the brother did of helping to arrange his
sisters’ marriages was a righteous deed and an act of obedience for which he
will be rewarded. What the brother did must be one of two things: 

1.

Either he did it by way of voluntarily helping his father to
prepare his sisters for marriage, or he did it as an act of kindness and
upholding ties of kinship with his sisters. In this case it is not
permissible for the son to ask his father or his sisters for anything of
that by way of compensation for what he spent, whether it is directly from
the father’s wealth or from his estate after he dies, because he only did
that by way of kindness and giving a gift, not by way of seeking
compensation. Al-Bukhaari (2589) and Muslim (1622) narrated that Ibn ‘Abbaas
(may Allah be pleased with him) said: The Prophet (blessings and peace of
Allah be upon him) said: “The one who takes back his gift is like the dog
that vomits then goes back to its vomit.” 

The father likewise has no right to favour him in gift-giving
because of that, because the son only did that by way of kindness, and there
is nothing to indicate that he should favour him in terms of gift-giving
over the rest of his siblings. 

Ibn Qudaamah (may Allah be pleased with him) said: The
individual must treat his children fairly in terms of gift-giving, so long
as there is no specific reason in the case of any one of them that makes it
permissible to give him or her precedence. If he does single one of them out
for a gift or give more to one than the others, then he is sinning, and he
must treat them all equally in one of two ways, either by taking back the
extra he had given to some and not others, or by making it up to the others.
Tawoos said: That is not permissible, even if it is the matter of a burnt
loaf of bread. This was also stated by Ibn al-Mubaarak, and something
similar was narrated from Mujaahid and ‘Urwah. 

End quote from al-Mughni (5/387) 

Please see also the answer to question no.
22169 

The scholars of the Standing Committee (16/207) were asked:

I fear Allah and I know that death is real and inevitable,
but my mother owns a small house, which I rebuilt, and I have a brother who
did not join me in that at all, but he upsets my mother and my father great
deal, and he has been treating them badly all his life, until now. Now he
lives outside the home, and my mother got angry and decided to register the
house in my name. I argued with her a great deal, but she is insisting on
registering it in my name. Now I am wondering: is my mother committing any
sin by registering the house in my name and depriving my brother of it? Will
I be committing any sin if I accept this from my mother? 

They replied:

If the situation is as you describe, then it is not
permissible for your mother to give you the house and not your brother,
because the Prophet (blessings and peace of Allah be upon him) said: “Fear
Allah and treat your children justly.” And there are other, similar
hadiths. 

If she does what is mentioned, then she will be sinning and
you will be sinning, because by accepting that from her, you are
participating with her in the sin and transgression. Allah, may He be
glorified and exalted, has forbidden that, as He says (interpretation of the
meaning):

“Help you one
another in Al-Birr and At-Taqwa (virtue, righteousness and piety); but do
not help one another in sin and transgression”

[al-Maa’idah 5:2]. 

She has to take back this gift or give the other son
something equivalent to it. If you see that she is insisting on not
including him with you, then there is no reason why you should not accept
the gift and give half of it to your brother, so that you will have done
what is required of you, if she does not have any children other than you
two.

Standing Committee for Academic Research and Issuing Fatwas 

Member… Vice President… President

‘Abdullah ibn Qa ‘ood… ‘Abd ar-Razzaaq ‘Afeefi… ‘Abd al-‘Azeez
ibn ‘Abdullah ibn Baaz 

2.

Or this brother spent on them with the intention of claiming
it back, so the father may give him some of his wealth, or leave
instructions in his will that he be given as much as he had spent, even if
he does not give the other siblings something similar, and even if the other
siblings do not agree to this giving, because what the father gives in this
case does not come under the heading of gift-giving or favouring one child
over the others; rather it is a kind of paying off a debt and repaying the
one who gave something as much as is due. 

The scholars of the Standing Committee (16/205) were asked: 

I have a father who is elderly, approximately seventy-five
years old, and he is still living. He had a house built of mud which is old
and in a good location. I demolished the house and rebuilt it with
reinforced concrete at my own expense; I have rented out the house and from
the rent I am paying instalments to some people to whom I still owe money.
Please note that I did not borrow anything from the real estate development
bank. My father wants to transfer ownership of this house to one of my
children, who is over seven years old. Please note that my father has me and
five daughters, and one of his daughters is older than me, and the rest are
younger. I am the one who has been sponsoring my father and my mother for no
less than fifteen years. 

They replied: 

Having reflected on what you mentioned about your son, to
whom ownership of the house will be transferred by your father, not being in
need of it at present, and that you promised your father, if he gives the
house to your son, that you will build a another house for your siblings at
your own expense, and that you have five sisters who are married, and that
you previously rebuilt at your own expense your father’s house that he
intends to give to your son – this indicates that his real intention is to
give the house to you, and to single you out for that to the exclusion of
your siblings. Rather he named your son as the recipient as a kind of trick.
Therefore it is not permissible for your father to give the house to your
son, because the Prophet (blessings and peace of Allah be upon him) said:
“Fear Allah and treat your children justly.” With regard to what you said
about spending on your father’s house, if you did that voluntarily and
willingly at the time of spending, then Allah will reward you, and you do
not have the right to claim it back from your father. 

But if you spent on it with the intention of claiming it
back, then you have the right to do that, but it is better for you not to
call your father to account for it and not to feel that what you spent on
him was too much, for your reward with Allah, may He be glorified and
exalted, will be greater than you expect, if you are sincere towards Him,
may He be glorified and exalted. 

And Allah is the source of strength. May Allah send blessings
and peace upon our Prophet Muhammad and his family and companions.

Standing Committee for Academic Research and Issuing Fatwas 

Member… Vice President… President

‘Abdullah ibn Qa ‘ood… ‘Abd ar-Razzaaq ‘Afeefi… ‘Abd al-‘Azeez
ibn ‘Abdullah ibn Baaz  

For more information, please see the answer to question no.
131901

And Allah knows best.