Regarding the cheque bounce what to do

Hello, We(my family) found a buyer for our property in December 2016 for our land. Total amount is 40 lakhs. We have taken 15 lakhs loan on that property in 2009 and paying the installment regularly. As per the talks between buyer and my family, he is supposed to pay us 20 lakhs(every year 5 lakhs) and pay the bank loan after registring the land in his name. Now he is postponing the registration saying that he is busy. In between, we asked him to pay cheque, so that we will have a guaranty. He gave 4 cheques each with the value 5 lakh. In those cheques first one is dated Juy 1, 2017. The second, third and fourth cheques have the same date and years are 2018, 2019,2020 respectively. Now, the bank manager is calling us to pay the yearly installment for the loan otherwise, land will be seized. We informed the buyer to make the registration soon or at least pay the bank installment first. He is still lazy. How can I deal with this? Do I have the right to put the cheque in bank in July?