Question: Is it allowed for my father to divide his land between his sons to the exclusion of his daughters before his death?
Answer: The one who divided his wealth (land) between his sons before his death and he is of sound mind and did not give anything to his daughters he has sinned twice:
First: when he divided his wealth before his death to deprive his daughters from inheritance after his death.. The reality one can see from the question indicates this.
Second: during his life he gave his wealth to some of his children to the exclusion of others. Both are Haraam. As for the inheritance Allah (swt) has defined and divided it for boys and girls the ayahs pertaining to this are clear.
As for giving the wealth to some children and not to others this also contradicts the hadith of the Messenger of Allah which stipulates the following:
Nu’man b. al-Basheer narrated that his father took him to the Messenger (saw) and said: Bear witness (o prophet) that I have given such and such part of my wealth to Nu’man. The Prophet said: have you given a gift to all your children like what you gave to Nu’man? He said: no. The prophet (saw) said: Then get someone else to witness this (because I do not want to witness unfairness).' Then he added, `Would you not like all your children to treat you with equal respect?' Basheer said, `Of course.' The Prophet (saw) told him, `So do not do it.’
In another narration Nu’man b. Basheer narrated that his father gave him a slave and that he came to the Messenger so that he would bear witness. The Prophet asked: did you grant this to all your children: he said: no. The Prophet (saw) said: ‘then take him back.’ Reported in the Sunan of Ibn Majah, Ahmad, Muslim, Abu Dawud with various narrations.
عن النعمان بن بشير قال: انطلق به أبوه يحمله إلى النبي r فقال: اشهَدْ أني نحلت النعمان من مالي كذا وكذا قال: «فكلّ ولدك نحلت مثل الذي نحلت النعمان؟» قال: لا. قال: «فأشهِدْ على هذا غيري» قال: «أليس يسُرك أن يكونوا لك في البر سواء؟» قال بلى. قال: «فلا، إذاً»
» وفي رواية أخرى عن النعمان بن بشير أن أباه نحله غلاماً، وأنه جاء إلى النبي r يشهده فقال: «أكُلَّ ولدك نحلته؟» قال: لا. قال: «فاردده»
Thus, in respect to your father gather your brothers and inform them that each one should give a third of what he has taken from the land to his sister as long as there are 5 sons and 5 daughters. For the male is the same (inheritance) as two females.
Remind them to fear Allah and to show respect to the father by lowering the sin from him so that maybe Allah will forgive him. If they refuse then distribute a third of the land which you took amongst your sisters so that they are happy.
This is if the inheritors of the land which your father distributed consist of 5 sons and 5 daughters.