Exchange and transfer of land

My case is some complicated so explaining with example. A person P was owner of property no 60 and 10. He sold half of the part to person M from property no. 10. After few years when person P died, the half of the remaining property no 10 and full part of property 60 transfer to his two son A and S. A and S exchanged their property no 60 with their father’s sold property to M under registered exchange. Now A and S become full owner of property no 10. Then my father bought half of the part of property 10 from S through registered sale deed from S. after our possession person M file a case in revenue court against A and S to take back the exchanged property. As S don’t had any interest in property 10 he didn’t appear in the court and the revenue court cancelled the exchanged. When my father raised the objection after hearing the news they told my father that he can continue your possession On half of the part of property. M also manage to change entry in revenue documents in which half part shows M name and half part to my father name and some part to A without physical possession (area also manipulated). Now after 20years A claim half part in my father’s part and secretly sale to N. now N is fighting us to take half part in my father share. Pls advise what to do.