Very Old unregistered property

My father purchased a property in resale (Builder to 1st owner, 1st to 2nd owner and 2nd owner to my father) in Pune in 2002, my father payed the stamp duty, however did not register the property. My father passed away in 2013, the person from whom my father purchased the property has also passed away..My father before he passed bequeathed the property in my name through a will, Will is probated as well. The society share certificate name has been transferred in my name. Only the sale document 1st to 2nd owner is registered. Builder to 1st owner and 2nd owner to my father is unregistered. How can I register the property now? Do I need to pay stamp duty again? Can I sell the property? I want to sell the property, the intended purchaser needs to take a loan on the property? Is it possible to get the papers in order and clear legal owner and title?