After father death man asking back loan given to dad no idea about it

Sir My father passed on 25 october 2015. He was self employed. I am working on a small salary. After his death a person came to us saying that he had given a loan of Rs 500000. We do not have any information about this loan. He has shown few undated cheques issued on his name. Now he is threatening us that he would take us to court and Sue us. I am only earning and we are 4 people. My mother, my 25 year old sister and my 13 year old brother. My father has 1 acre land inherited from his father. Will an action taken against us as property is the only support for my brother future studies.