Will-probate

Restected sir, I am Ram NRI -Singapore.Some property issue in chennai.My Father(Late) purchased land in his our hard earned income in my mothers name ( Late) and in the year 2001 and constructed the flats.he has made WILL in the year 2001 and duly registered the WILL in Honorable court of Chennai in the year 2001.We are 4 , ie two elder sisters , myself and my younger sister.My father passed away in the year 2014.So in the WILL he mentioned very clearly that he has 3 daughters and one son and 3 daughters well educated, well settled and duly married with lot of finance assistance.So my father clearly states that since i have done a lot to 3 of my daughters, after my death the entire property will go to my one son Ram and my 3 daughters has no rights to claim legally .But now my 3 sisters arguing that they will not accept the WILL and they will not agree for probate My Question is As per Hindu Succession act Amendment 2005 is their argument correct ??Euqla rights to SON/Daughters??? Is their any validity or expiry of WILL Do i need to Execute the WILL ( Go for probate )immediately or i can do later stage?? I came to understand that i must execute the WILL within 3 years of my father date of death .Is it so?? Is it worth for me challenge my sisters in the Honorable Court of Chennai ?? Please guide me