Legal Notice Ground Money Borrowing

Sir, I need your help. My mother, she died due to covid last month and I'm a student right now. My mother may have took money from different person for whatever reason and in return she had given my dad signed cheque to that person butmy dad didn't signed the cheque for that transection. He gave that cheque to my mother for money transfer to his account to hers. We don't know all money borrowing things because this isn't happened in front of us. I was studying in a different district and for dad he don't know anything because he was not present in all money borrowing nor she told us anything. Now person giving legal notice to us. What should we do now? some of the person doesn't have legal agreement of the transactions which they had given to my mother and they claimed they had given in cash. In what basis we can rebate those claims. Sir I'm fed up all these affecting me I can't continue my studies. Help me. Very urgent sir.