Partition Deed between brothers

We (6 brothers) have given our property to developer who has already build a flat on the said land. As per the agreement we have received 6 flats and 4 garage for 6 brothers of us. Hence flat has been divided equally and 2 of my brothers are not interested in garage hence mutually they have given to us. However as per the possession letter from developer, he has mentioned total 6 flats & 4 garages but it doesn't mention any specific owner details. Hence we want to execute a mutual partition deed so that each one of us legally have their portion. Each of our flat is 1000sq feet and costing 4000 per sq feet as per current market. we would like to know how much it will cost us from govt side. As per information on this site, 0.5% stamp duty + 1% registration we have to pay based on the value of the property+ the legal charge. My question is here, what is the property value? will it be total 6000 sq feet or value of any one flat which is 1000 sq feet. None of the answer in this site has this information. So again the question is value will be based on one flat or all flats?