All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
If your father wishes to divide his property among you during his lifetime, then this is not considered a division of inheritance, as the division of inheritance must be done after the person's death. Rather, this is a gift, since it is done during his lifetime. Therefore, the father is obliged to observe justice and equality among his children, sons and daughters alike, in terms of gift-giving. The Prophet, sallallahu ‘alayhi wa sallam, said, "Fear Allah, and observe justice and equality among your children." [Al-Bukhaari and Muslim]
Scholars held two views regarding the manner in which justice among one’s children concerning gifts is accomplished; whether to give the female the same share as the male, or to give the male twice the share of the female like inheritance. The opinion that is most likely correct and the one adopted at Islamweb is the first one, so the father should give his sons and daughters equal gifts.
As for the house that your two brothers built with your father, if your brothers contributed to the construction of the house as a gift with the intention of donating their money and not with the intention of sharing its ownership with him, then it is the property of the father. The fact that they helped him does not warrant favoring them over their siblings in terms of gift-giving, and they shall earn the reward for having helped him from Allah. However, if they contributed to the construction with the intention of being partners with him in its ownership, then they are considered his partners and are entitled to shares in proportion to their contribution. Your father has no right to favor them in terms of gift-giving regarding the rest of his property. Rather, they are entitled to their due shares of the house which they contributed to in its construction in proportion to their contribution.
Also, the land on which your younger brother is building, if his father gave it to him as a gift, then he is obliged to give his other sons and daughters equal gifts to observe justice among them in this regard. He is required to give each son and daughter an equal piece of land or its monetary value in order to comply with the obligation of upholding justice and equality among children in terms of gift-giving. However, if he permitted the younger brother to build on this land without intending to offer it to him as a gift, then the house is considered ‘Aariyah (a borrowed item) that expires with the death of the father. After his death, the land becomes part of the inheritance and is divided among all the heirs. The son who built his house on this land does not own this land. The value of the building should be estimated - scholars held different views as to whether its value should be estimated while standing or demolished, and the rest of the heirs should pay this son the value of the building, and they are all entitled to it (the building).
As long as the father is still alive, he should clarify his intention regarding the gifts in order to avoid disputes among the heirs after his death.
As for the deceased person who has no other heirs entitled to inherit other than a wife, five sons, and three daughters, the wife is entitled to one eighth of the estate, and the remainder of the estate should be divided among the sons and daughters by virtue of Ta‘seeb (by virtue of having a paternal relation with the deceased and not having an allotted share, so they get what is left after the allotted shares are distributed); and the male gets double the share of the female.
Allah knows best.