Cancellation of sale of agreement

Sir I am going to buy property which was already had agreement with builder. HDFC Bank had given finance to the 1st buyer and he have close the loan with NOC from bank. Right now, Status of building is under construction. Now if I would buy this flat, I will be the second owner of the property. Instead of going into the chain agreement, I have requested to the builder that I am interested to buy flat from builder directly if 1st buyer not in picture. In this scenario, builder has proposed below mentioned solution to me- 1) The 1st buyer will cancel sale of agreement between him and builder then flat entry will come in the leadger of builder. 2) After cancellation of 1st owner sale of agreement, builder will sign sale of agreement with me. My question 1) Is there such provision in law so that 1st buyer will cancel his sale of agreement mutually with builder? 2) Is it will be legally title clear property to buy from builder? 3) Will 1st buyer claim on this flat after my agreement with builder? Expert pls comment