The sellers appear to be at fault
Even if a higher TDS is deducted it's not that that money is lost
The seller can always claim a refund from the IT department
The seller's argument that they have lost rent for 2 months is also preposterous
They are already sitting with your 7 lacs deposit and earning interest on it and they have not taken any prompt steps to get the certificate for reduced TDS
You will have to file a suit for avoidance of contract and for refund of your 7 lacs with damages and compensation
I presume what has been registered is an agreement to sell and what is pending is a sale deed and not a sale agreement. There is a world of difference between the two
If the agreement to sell is registered and if a cancellation deed is not registered then the brothers will not be able to resell their property
Also when the brothers cannot pursue refund of the TDS from IT, its highly unlikely that they will also file any suit for specific performance against the buyer
As there is a deadlock there is no way out but to file a suit.
May be on receiving the court summons with the suit papers the brothers would come in line and settle the matter with you amicably
If a suit is filed and when there is an agreement for sale which is registered and not cancelled, then the brothers are essentially locking up their property in dispute, which would be quite foolish as no purchaser will then put their hands in such a property
So the way out is to incur some expenses and file a suit to avoid the contract as above and see how it pans out
Begin with a legal notice