Bought flat which is not registered to me can i further sell it

Sir, I have purchased a flat three years back. After making the Purchase Agreement(between me and the builder), I paid the entire price of the flat to the builder. The builder has given me the possession of the flat. The REGISTRY of the has not been done. Now i want to hand over/sale the said flat to my close relative by taking the current price of the flat. I have made a TRIPARTITE AGREEMENT (among me, my relative and the builder) mentioning all the details. Here, builder will be the "CONFIRMING PARTY" . He will ensure that the REGISTRY OF THE FLAT will be done to the current purchaser i.e. my relative. Thus, i will save my registry cost but will pay the LTCG as applicable. I want to know that the above process is legal or not. Here I want to tell you that the Bank is ready to give loan to my relative on the basis of above TRIPARTITE AGREEMENT. Kindly solve my problem so that i can save my registry cost.