All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It seems that your father made a will in which he specified that piece of land for his four minor sons in order to be able to marry. Since they are legal heirs, this will is invalid. In a Hadeeth, the Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said: “Allaah Gave each one his right so there is no bequest for an heir.” [Ahmad, Abu Daawood and Ibn Maajah; Al-Arnaa’oot: Hasan; Al-Albaani: Hasan Saheeh]
The Hadeeth indicates that a bequest for a legal heir is impermissible, unless the other heirs approve it, on condition that they are right-minded adults.
Consequently, if you all approved the bequest of your father, the piece of land is to be given to your young brothers. However, if only some of the heirs approved, the bequest will be taken from the shares of those who approve. If all the heirs disapprove the bequest of their father, that piece of land will be added to the rest of the estate and the whole estate will be distributed among the heirs, males and females. If you are six males and five females and there are no other heirs, the male will be given twice the share of the female, according to the Quran. Consequently, the total shares in this issue are 17, two shares for each male and one share for each female.
If you approved the bequest of your father, the piece of land is given to the four minor brothers and the rest of the estate is distributed according to the aforementioned manner.
Whether one or all of your older brothers assume the marriage costs of their young brothers, or some of them does not change the ruling. If they did so on the basis that it is a donation or gift, then they are not entitled to restoration. If it is a loan, they are entitled to restoration when the time is due.
Allaah Knows best.