About ipc 420

Good morning sir my brothers purchased 12 guntas land in 2010 and sold to one person in 2015 ,the person agreed to buy the land for 42 lacks and gave 12 lacks as advance. The person failed to pay the total amount within the date .our sale deed time us 90 days , we waited for 5 months.after that in presence of a mediator the person agreed that he cannot pay the remaining amount and asked his amount after sale.we sold the land to other person 36 lacks, who know all these things and he gave paper publication and got registered .we called the 1 St person to take back his advance in presence of mediator ,we asked him the 1 St person that we lost some money due to you so we asked him to take 8 lacks but he asked 12 lacks and interest .we refused that and he filed a case 420.my innocent brothers don't know any legal procedures and we came to know lately that the 1 at person is a land broker and he don't buy land own just within the given time he sells to another party....please give me a suggestion what we have to do .... Regards K S Krishna