Sale of Property without Partition Deed

Hello! My father inherited a property in Kolkata. We had a two floor old house in Kolkata in the name of my grandmother. Two years back it was mutually agreed between my grandmother and her four children ( My father, my uncle and my two aunts) to give the old building to promoter and then get 4 flats out of it- for my father, my uncle, my older aunt (this was a to be a shared property between my aunt and grandmother) and my younger aunt. Now each one as was discussed have got the possession of their flats. All my other relatives made moved in. My father instead wanted to sell his flat, but to do that our lawyer is saying we need a partition deed to be signed by all the parties. My younger Aunt has now at this point have disagreed to sign the partition deed. Is there any other way to sell the property without getting the partition deed signed? At this point we are neither able to sell the property, or to get its registry done in our name so that we may rent it. Please help us with a way.