Relinqushment deed

I have purchased a real estate land in my name and my mother's name (50% ownership each). The property was never fully transferred in our name as before doing the registration another party has claimed rights on it and there is a ongoing civil court dispute going for the past 18 years. My mother has passed away without any will and my 2 brothers & 2 sister's have been added as legal heirs to this property. I am fighting the civil dispute against the 3rd party in the courts for past 18 years and no one in the family has any connection with the original property purchase or the ongoing civil dispute. However since the new legal heirs have been added on my side, to avoid further complications, we want to get a relinquishment deed so that my brothers & sisters relinquish their rights on this property and I become the sole owner. How can I get this deed done ? Does a "notarized hakk sodd patra" on stamp paper eligible ? If it needs to be registered, what stamp duty & fees are required to be paid since the property isnt even registered in our name yet due to dispute. we only have a "sathe khat" (agreement to sale) for the original purchase.