Sale of House property from Seller to First Buyer and then by First Buyer to Second Buyer

There is a house property on a Govt leased land that is further subleased and developed. One of the apartment is owned by "A " who has a registered Sale Deed in his name. "A" has entered into a sale agreement with "B" for sale of the house. B has paid majority of the due consideration amount, retaining some amount ( 5%) till the Sale Deed execution and registration as per the agreement terms. However, the govt has temporarily stopped registration of such leased property . Now due to some financial reason "B" need to sell this to "C" and both have agreed to a sale amount to be paid and other Terms & Conditions. Under this circumstances, as B is not yet owning the house, it is suggested to have a tripartite agreement between "A" , "B" & "C" laying down the facts and covering the following a) A would agree to register the Sale deed between A & B as and when the registration is started by the Govt. b) A will have his No Objection to the proposed selling by B to C . c) B & C to enter into a separate Sale Agreement with detail Term & Condition on the completion of a) & b) above. Please let us have your comments & suggestion on the above proposed action.