Is it possible to claim any compensation?

My grandfather had ancestral property in Chennai. It is not self acquired. He had 5 children - 3 daughters and 2 sons. He made a will that after his death both sons should enjoy property. In 2005 amendment to property act was to be enacted where daughters also have equal share. Knowing this information, the eldest son enacted drama in family stating he is about to take loan for business and if he defaults entire father property will be confiscated by bank. So he told sisters that he wanted to safeguard them and ask them to sign in papers. He took them to registrar office each seperately and in urgency took their sign. He never shared the document details with sisters till date. He arranged own witness signatures. He also did not inform his sisters sons or husband of the same or took them along while taking signatures of sisters on documents. Now in year 2022 he started construction in this property and sisters asked him their share. He said they have already signed settlement deed in 2005 and he will not give any share. Believing their brother they had signed in year 2005, but they realised they have been fooled as now only they came to know that he has made them sign in settlement deed. If will was made by father then why he did not probate the will? Knowing that for ancestral property father's will is not valid, he has cheated his sisters along with his younger brother. He has also completed the construction now. 1st sister is retired state govt employee and has 2 sons. 2nd sister was employee of state controlled Co-optex. Her husband is unemployed and only son committed suicide. 3rd sister is divorced and has no issues. Sisters 2&3 have no one to take care. Also all 3 sisters are senior citizens now. Now on what grounds can the sisters or their children claim compensation for this injustice meted out to them?