His grandfather left instructions that the females should be deprived of their inheritance; should they follow this with regard to their father’s legacy?
Question

                My grandfather left a will stating that the males were to be given and not the females. I cannot find any will for my father, so should we act in accordance with my grandfather’s will?.
Praise be to Allah.
      Firstly: 

    A will which deprives the females of their inheritance is an 
    unjust and haraam will, because it is contrary to the division of the estate 
    as enjoined by Allah, may He be exalted, in His Book, and He issued a 
    warning to the one who goes against that. Allah says concerning inheritance 
    (interpretation of the meaning):

    “These are the limits (set by) Allaah (or ordainments as 
    regards laws of inheritance), and whosoever obeys Allaah and His Messenger 
    (Muhammad صلى الله عليه وسلم) will be 
    admitted to Gardens under which rivers flow (in Paradise), to abide therein, 
    and that will be the great success.

    14. And whosoever disobeys Allaah and His Messenger 
    (Muhammad صلى الله عليه وسلم), and 
    transgresses His limits, He will cast him into the Fire, to abide therein; 
    and he shall have a disgraceful torment”

    [al-Nisa’ 4:13, 14]. 

    It is not permissible for the heirs to act upon this unjust 
    will; rather they have to give the women their rightful share of the 
    legacy. 

    It should be noted that it is not permissible to bequeath to 
    heirs, whether male or female, because of the report narrated by Abu Dawood 
    (2870), al-Tirmidhi (2120), al-Nasaa’i (4641) and Ibn Maajah (2713) from Abu 
    Umaamah (may Allah be pleased with him) who said: I heard the Messenger of 
    Allaah (blessings and peace of Allah be upon him) say: “Allaah has given 
    each person who has rights his rights, and there is no bequest for an heir.” 
    This hadeeth was classed as saheeh by al-Albaani in Saheeh Abi Dawood. 

    This will should not be executed except with the consent of 
    the heirs, because the Messenger (blessings and peace of Allah be upon him) 
    said: “It is not permissible to make a bequest to an heir unless all the 
    heirs agree.” Narrated by al-Daaraqutni; classed as hasan by al-Haafiz Ibn 
    Hajar in Buloogh al-Maraam. Ibn Qudaamah (may Allah have mercy on 
    him) said in al-Mughni (6/58): If he makes a bequest to his heir and 
    the other heirs do not allow that, it is not valid, and there is no 
    difference of opinion among the scholars concerning that. Ibn al-Mundhir and 
    Ibn ‘Abd al-Barr said: There is consensus among the scholars concerning 
    that. There are reports from the Messenger of Allah (blessings and peace of 
    Allah be upon him) to that effect. Abu Umaamah narrated: I heard the 
    Messenger of Allaah (blessings and peace of Allah be upon him) say: “Allaah 
    has given each person who has rights his rights, and there is no bequest for 
    an heir.” Narrated by Abu Dawood, Ibn Maajah and al-Tirmidhi. … If they do 
    allow it, then it is permissible according to the majority of scholars. End 
    quote. 

    Based on that, if the grandfather made a will to his male 
    sons, this is a bequest to an heir, and should not be executed except with 
    the agreement of the other heirs, namely the females. 

    Secondly: 

    Your father did well not to make a bequest to any of his 
    heirs. If the deceased did not make any bequest then none of his heirs have 
    the right to make a bequest on his behalf, so how about if he wants to make 
    an unjust and unlawful bequest? What you have to do is to divide the estate 
    as commanded by Allah, and give each person his rights. 

    And Allah knows best.