Do the grandchildren get anything from the estate due to the law of binding wills (wasiyah waajibah)?
Question

                A woman died, leaving behind a husband, three sons and a daughter. She also had the children of a  deceased fourth son, a son and two daughters. My question is: Do the children of the deceased son inherit? How valid is the so-called law of binding wills (wasiyah wajibah)? Please note that the deceased lady died and did not bequeath anything to them. Is there any advice you can offer to the children of the deceased son?.
Praise be to Allah.
    Firstly: 

    When a person dies, his estate is to be divided among his 
    living heirs only. There is consensus on this point among the fuqaha’. Hence 
    the scholars have stated that one of the conditions of inheritance is that 
    the heir be alive after the person dies. 

    See: al-Mawsoo’ah al-Fiqhiyyah (3/22). 

    So the fourth son, who is deceased, has no share of the 
    estate. 

    His children do not inherit either, because the grandchildren 
    do not inherit from their grandparents if any of their paternal uncles are 
    alive, according to scholarly consensus. 

    See: al-Mughni (9/22) and al-Tahqeeqaat al-Mardiyah 
    fi’l-Mabaahith al-Fardiyah by Shaykh Saalih al-Fawzaan (p. 114-115). 

    Based on this, the children of the son who died before his 
    mother’s death do not get anything, because they are prevented from 
    inheriting by the presence of their paternal uncles. The estate is to be 
    divided among the living only, namely: the husband, the three sons and the 
    daughter. The husband gets one-quarter because there are  descendents of the 
    deceased, and the rest goes to the sons and daughter, with each male getting 
    the share of two females. 

    Secondly: 

    It is mustahabb to give the children of the deceased son 
    something of the estate, either as a bequest from their grandmother before 
    she died, so long as it is not more than one-third, or by their uncles and 
    aunt giving them something, so as to soften their hearts, especially if they 
    are in need. 

    In the answer to question no. [Ruling on the binding will 
    (wasiyah wajibah)], we have stated that the law on the binding will (wasiyah 
    wajibah) is invalid, and that wealth taken by means of it is haraam wealth. 

    Thirdly: 

    Our advice to the children of the deceased son is to fear 
    Allaah and beware of consuming wealth unlawfully, because they have no right 
    to this estate, as stated above. The Prophet  (peace and blessings of 
    Allaah be upon him) said: “It is not permissible to take the wealth of a 
    Muslim unless he gives it willingly.” Narrated by Ahmad (20714) and classed 
    as saheeh by al-Albaani in Saheeh al-Jaami’ (no. 7662). 

    And he  (peace and blessings of Allaah be upon him) said: 
    “Every body that is nourished from haraam sources, the Fire is more fitting 
    for it.” Narrated by al-Tabaraani and Abu Na’eem from Abu Bakr (may Allaah 
    be pleased with him), and classed as saheeh by al-Albaani in Saheeh 
    al-Jaami’ (no. 4519). 

    They should understand that the ruling of the court is 
    contrary to sharee’ah, and it is not permissible for them to take this money 
    or for them to ask for it or to compete with the heirs for it. 

    Our advice to the judges is to reject this law and disavow 
    themselves of it, because it is a transgression and it is implies correcting 
    the division of the estate that Allaah Himself has decreed.  

    With regard to the heirs – the husband, sons and daughters – 
    they should willingly donate some of the estate to the children of their 
    deceased brother, so as to maintain ties of love among them and soften their 
    hearts, especially if they are poor.  

    We ask Allaah to help us all to do that which He loves and 
    which pleases Him. 

    And Allaah knows best.