Right of Heirs in Property redeveloped under SRA Act

My Father had acquired a Tenancy Room in mumbai for which Payment was been made by my mother from her elemoney at the time of taking the tenancy right , We were having Tenancy (Rented Room in my father's name in mumbai) Simultaneously in 2002 Landlord approached my Father-Mother along witth other members of chawl , area with a offer to Redevelop the property under SRA Scheme and a Building constructed under SRA Act my father had accepted offer jointly with other members on 19/01/2003 there after as per "Kararnama" signed by my father dated 14/10/2003 according to which He named the Persons Occupying Rooms where in He mentioned Name of Himself my Mother , Myself Age 43 years (Yonger Son) my wife & My Son (Minor) My Father Expired on 25/0302006 intestate We , My Elder married Sister,My Elder Brother and My self had via a Relinquished Deed executed on Rs.100- Stamp Paper dated 20/04/2007 , Relinquished released & Surrender our rights, share Title and interest in favour of my Mother. She had Got Possession of Flat Re devloped & Constructed under SRA Scheme dated 13/07/2007 Now My sister due to Pressure of My Brother in Law had sent a Letter via Advocate demanding her share Please give your Guidance/Suggestion my email id is hirent31@yahoo.co.in