Dought & clear - The heirs do not have the right to take back from their sister’s children a gift that she received from them withtheir consent, then her children inherited it.

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 tosharee'ah, because it is
abequest to an heir. But ifthe 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 madethe 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.,
afterthe 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 beforethe death of the
beneficiary [your mother] or after her death, and whether that was
before you disposedof this land or afterwards, because their agreement
to the execution of the bequestmeant 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.
And Allah knows best.