Cancellation of notary agreement for land

Sir, My father had done land deal with a party via notary agreement on 13.10.16.Bayanya of 30lakhs recived on the date of notary agreement. It is mentioned in the agreement that 62.8 lakhs will be paid on 15.12.16.rest balance i. e. 2.7crore will be paid at the time of registery on or before 15.1.18. But party not paid 62.8 lakhs on date mentioned in notery agreement due to demonitization issue. On humanitarian ground verbely we agreed to accept the due amount within the next three months. Party paid only 50 lakhs within the time framed extended on verbal request. When asked for 12.8 lakhs due they were asking for more time. But they even not paid the due after next three months and asked us to provide land measurement report from Patwari. We have already given them registery, dakhil kharij and 143 (land use change agri to resedancial), naksha etc. Finaly after serving 3 notice thru advocate we cancelled the notery agreement deal. Now they are saying that they will go to court. My questions are 1)we are agreed to return there money 60 lakhs as 20lakhs we lost in some of our deal which we lost due to not receiving the money from there side .Have we have to pay them back all (30lakh bayana +50 lakh) i e 80lakh. 2)Is cancellation from our side OK. 3)If they file civil case then what will be the expected time for the judgement. And can court order us to sell them the land at the same price as mentioned in agreement today after the judgement .party is not taking money back and that money is in capital gain account. If party not take back then income tax will treat this as income and tax on the amount @30percent.Can we submit this in court in case party refused to take back. Pl provide valuable inputs Regards .