Stamp duty on lost documents

I have a industrial gala in Sakinaka Mumbai. Now initially the owner(xyz) purchased the property from builder in 1973 and also had lost the original agreement. In 1975 we purchased the property from xyz by making a partnership deed on stamp paper (no sale deed was made) where our our 4 family members where included as partner with xyz. In 1976 xyz was retired from that partnership by paying some amount and we became the owner. From 1976 till 2000 several partners where included and retired which were all family members and for all transaction partnership deeds were made in stamp paper which were not registered. In 2000 by same process my grandfather became the sole owner and after that my grandmother and after that there 5 legal heirs. Now we executed a registered release deed in which only 2 legal heirs were made the owner and remaining 3 were removed. Now one of the two legal heirs want to become the owner. So now my question is will I have to pay the old stamp duty? On which document should I pay the stamp duty as original documents are lost by previous owner? Will there be a problem to sell the property in future? Right now we only have 2 documents for our property share certificate in the name of 2 legal heirs and a release deed.