1. If you have already agreed for paying 33% to the seller, then it is upto the seller how he applies the said amount. Whether its for repayment of his existing loan on the flat or for something else
2. in case the seller fails to complete the transaction as agreed in the agreement to sell, you will have your remedy against the seller under the specific relief act by seeking specific performance of the contract
3. i suggest you first ask the seller what is the total outstanding loan on the flat you intend to purchase and whether the 33% which you will be paying would suffice to close that loan account and get the property papers released from bank
4. if the 33% of consideration corresponds to the balance loan amount then you can directly pay to the seller's lender bank on behalf of the seller, instead of paying to the seller
5. you must record all this clearly in a written understanding like your agreement to sell and also set out the consequences in the event the seller fails to obtain a clear title for the flat by having the mortgage discharged
6. yes the NOC of mortgagee bank will be needed before you and seller sign the sale agreement. But if you are signing a MOU with the seller then that wont be needed because under the terms of the MOU, the seller will have agreed with you to discharge the mortgage loan on the flat to be sold by applying the 33% money which you will be paying to the seller