Does he have to return the money that his brother spent on him?

Firstly:

Whatever your
brothers spent on you from the pension of your mother or your father, or
from other wealth belonging to your parents, they have no right to demand
any of it from you. This is quite clear.

Secondly:

Whatever your
oldest brother spent on you from his own wealth is subject to further
discussion.

1.

If your father
was in financial difficulty and unable to spend on you, and your brother was
well off, then he was obliged to spend on his father and his young
dependents, and those on whom the father is obliged to spend.

If he did that,
then he has no right to ask you for anything.

Shaykh al-Islam
Ibn Taymiyah (may Allah have mercy on him) said: The son who is well off
should spend on his father who is in difficulty, and his father’s wife, and
his younger siblings.

End quote from
al-Ikhtiyaaraat, p. 409.

2.

If your father
was well off, then your brother was not obliged to spend on you, and you do
not have to spend on him either, because he would not inherit from you if
you died.

In that case, if
he spent on you with the intention of upholding ties of kinship, he does not
have the right now to ask for anything.

If there is a
dispute, and the one on whom money was spent (the recipient) says that this
was upholding ties of kinship, but the one who spent on him (the benefactor)
says that he wanted to be repaid, then what counts is the statement of the
one who spent of his own wealth, provided that he swears an oath to that
effect.

Ad-Dardeer said
in ash-Sharh al-Kabeer (2/518):

In the case of
one who spent on a minor seeking repayment, if at the time when he spent on
the minor, the child had his own wealth or had a father who was well off,
and the one who spent on him was aware of that and swore that he spent on
him with the expectation that he would be repaid (then he has the right to
take his money back). However, there is no need for him to swear an oath if
there were witnesses.

But if the child
had no wealth at the time when the benefactor was spending on him, then the
benefactor has no right to demand repayment. End quote.

Ad-Dasooqi said
in his Haashiyah: If the recipient claims that the spending was by
way of upholding ties of kinship, and the benefactor claims that he did not
intend it by way of upholding ties of kinship – rather he expected to be
repaid or he did not have any intention in mind – then what matters is what
the benefactor says, provided he swears an oath to that effect, whether the
recipient was a wife or otherwise. So let him swear that he spent with the
expectation of being repaid, or that he spent and did not intend it as being
by way of upholding ties of kinship. When an oath is required is when the
benefactor has no witnesses to support his claims that he gave with the
expectation of repayment, otherwise there is no need for an oath. End quote.

It should be
noted that circumstantial evidence carries weight regarding this issue. If
the circumstantial evidence indicates that the spending was by way of
showing kindness to a relative, such as if he did not ask for his money to
be repaid for a long time, or he did not tell you to take money for your
needs from your wealthy father, then no attention should be paid to his
saying now that he spent with the expectation of being repaid and his
intention was to ask for repayment.

Al-Khurashi said
(4/196): Except if she gave it with the intention of upholding ties of
kinship, in which case she cannot ask for the return of what she spent on
her husband or on a non-mahram relative.

Al-‘Adawi said
in his Haashiyah: It should be noted that you can tell whether it was
spent by way of upholding ties of kinship through the circumstantial
evidence, so think about it. End quote.

All of this is
assuming that your father was well off when he spent on you.

If he was not
well off, then your brother’s spending on you was obligatory, as mentioned
above.

In the case of
it being permissible for your brother to request repayment of what he spent
on you, he should ask your father, not you.

You are not to
be asked to return anything to him, whatever the case.

But what appears
to be the case is that what is prompting him to do this is the dispute
between you and him, hence you do not say anything about your other
brother’s attitude concerning this issue.

Our advice to
you all is to reconcile amongst yourselves, and to remember that you are kin
and relatives; upholding ties of kinship is obligatory and severing those
ties is forbidden.

If you are able
to go for Hajj then you should hasten to do so, for Hajj is obligatory
immediately once one is able to do it, according to many of the fuqaha’.

And Allah knows
best.