rights of share of children of their deceased mother in the share of her alive father

I aged about 38 yes, married father of two daughters, profession tiffin supply, earning hand to mouth. For living small rented house..paying rent difficult. My father 71years retired, after retirement did business for & with me... Heavy loss.. Property auctioned by bank bcz loan taken against property for business were not paid in time. I have one younger sister now married with one daughter, but does not have her own house. My mother who passed away In January 2013..after long illness. My Nana g aged now 90yrs, (had two daughters & three sons, my mother was the eldest) ,have number of industrial and residen istial properties. My Nani passed away in 2010.He has given shares of all movable &immovable assets (two residential cum commercial buildings in New Delhi
Value more than 30cr,one Kothi in Noida value abt 10cr,factory value 25 cr & many hidden properties & bank deposits) to her four children and has not given any share to Me, & my sister.,the children of her eldest daughter, our mother who passed away in 2 013. All my three mama's and my Masi are already staying in their own houses and are financially very strong. WHY we are deprived of our mother's share.I f I ask for my and my sister's share ,he threatens that he will write a Will,in favour of his grandson,son of his eldest son.Kindly suitably guide & instruct. With hope and due regards.....