it is necessary to peruse agreement for sale executed by your father with purchaser to advice

2) it appears time was not essence of contract

3) it is well settled law that even if contract doers not provide specific period when payment is to be made balnce payment ought to be made within reasonable period of time

4) your father ought to have terminated contract if purchaser failed to make payment and should have refunded advance money received

5) better settle the matter amicably as litigation is long drawn affair

1. Since no date of execution of sale deed was mentioned in the agreement to sell it was incumbent on the buyer to have taken the steps to execute the sale deed within a reasonable span of time, say a year. However, before a fresh agreement to sell could be made with another prospective buyer your father should have cancelled the existing agreement with the previous prospective buyer.

2. Issue a lawyer's notice to the previous prospective buyer to cancel the agreement to sell and also file a caveat in the civil court so that you get an opportunity of being heard before the court passes an ad interim ex parte order.

The validity for a sale agreement is three years from the date of execution of the sale agreement, but this deed should be a registered deed.

If there is no time specified in the agreement, then it shall be valid only for three years, beyond that the buyer cannot enforce the sale agreement before court,.