Muslim sibling property dispute

My mother was born out of my grandmoms first marriage. My 2 step uncles out of her second marriage. My grandmom died in 2004, step grandfather died in 2000 and my unmarried step uncle died in 2007. The only 2 heirs are my mother and my married step uncle. The disputed flat in mumbai is solely in my grandmothers name. Despite various attempts my uncle refuses to settle this out of court. What is my mothers legal share as per mohammedan law? What is the best remedy to expedite a positive court ruling. She is a senior ailing citizen n needs the money urgently.