The heirs do not have the right to take back from their sister’s children a gift that she received from them with their consent, then her children inherited it
Question

                My Grandfather wrote a will giving 1/4 of his Land to my Mother and the rest to be shared egually amongst 7 Children and the Wife.They agreed to it and it was implemented some 14 years back. My brother and I inherited from our Deceased Mother 11 years ago. Now Our uncles and aunts want to contest the Will which they already accepted to whilst we have built a 2 storey building on some part of our mothers portion. Is it possible to cancel the inheritance when we go to the law courts according to islamic Law ?
Praise be to Allah.
      Firstly: 

    The will that your grandfather made to his daughter, who is 
    your mother, is not permissible according to sharee‘ah, because it is a 
    bequest to an heir. But if the other heirs agree to it, they have the right 
    to do so and it becomes valid to allow the bequest. 

    See question no. 
    174421

    Secondly: 

    If the one to whom the bequest was made died before the one 
    who made the bequest, then that bequest becomes invalid. 

    It says in al-Mawsoo‘ah al-Fiqhiyyah (43/273): 

    The bequest becomes invalid if the named beneficiary dies 
    before the one who made the bequest, according to the consensus of the 
    fuqaha’, whether the one who made the bequest was aware of his death or not, 
    because the bequest only becomes binding with the death of the one making 
    the bequest and the acceptance of the beneficiary. End quote. 

    But if the one who made the bequest [your grandfather] died 
    when the beneficiary [your mother] was still alive, and the heirs all agreed 
    to that bequest after their right to the wealth was confirmed, i.e., after 
    the death of the one who made the bequest, and your mother took possession 
    of that land based on their approval of the bequest, then your maternal 
    uncles and aunts have no right to take it back after having agreed to it, 
    whether that was before the death of the beneficiary [your mother] or after 
    her death, and whether that was before you disposed of this land or 
    afterwards, because their agreement to the execution of the bequest meant 
    that they gave up their rights to what was given to your mother. When the 
    recipient has taken possession of the gift, the giver has no right to take 
    it back after that. 

    See also the answer to questions no.
    166393 and
    137971

    And Allah knows best.