Property dispute

Sir/Mam, I have question and doubt regarding a property owned by my parents. from year 2002 some other person is trying to show the possession on the land registered under my parents name. that person even filed case in local court which was rejected and now he is trying to file the same case in high court. we wish to sell the property but because of the dispute going on we cant sell it. 1) my parents bought the land in 1994/95, even 7/12 is registered under their name and even they got loan from a well known bank for it. 2) we lived their for more 15 yrs. 3) in year 2002, one person tried to show possession over our land. but his case got rejected in local court so he went for high court. its just not our piece of property that he claims to be his but there are many more in same line of our house that he claims to be his. 4)all the legal deeds were performed and payment was done by my parents but still that person claims that property belongs to him. Sir/Mam, my doubt is if it was his land then why dint he appeared before when the land was sold to us. we have owned the land through legal procedures then why we have to take his permission and pay him some amount to sell our property. if the property was already in a dispute then why was our loan sanctioned and even our buyer's loan got sanctioned against our property. now the person claiming is asking us to do "sulainama" and asking for amount 12 lakhs+ for it. even we went to talathi office they said if you want to sell it then you have to take their permission. thank you. waiting for your reply.