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

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.