Sale dispute

Dear Sirs, My Grandpa has sold about 10 Cent (4356 Sqft.) of land to party-1(First Party) in the year 1985 from total extend of 2.54 Acres of particular Survey No. X, the sale has not been registered and there is no proper document for the said sale. Only document, Party-1 has that the sale particulars written in the 20rs Stamp paper (in the Year 1985) small chit (in the year 1990 and 1997 for additional piece of land) signed by My Grandpa. Party -1 has built a house and planted Coconut tree, had Electricity connection from 1992. Party-1 having, bill paid receipts of House tax and Electricity Bill etc. from 1992 to till date. In the year 2000, My Grandpa Expired. The past sale details not known to legal heirs (legal heirs are Grandma and Four Daughters) and the said legal heirs executed sale deed to the Party-2 (Second Party) from the Survey No X, in the year of 2007, the sale deed includes the extend 10 Cent of land which sold to Party-1 by My Grandpa.( Total Extend of Sale is 2.54 Acres of Survey No. X in the sale deed executed to the party-2). In the year 2014 My Grandma also expired. Now the Party-2 threatening the Party-1 in the sought of demolish the house and vacate the land. My Grandpa’s legal heirs tried to solve the problem amicably by repaying Cost of 6 Cent land but Party-2 demands 100 times more than the purchase cost. Party-2 is not ready for amicable solution and their only adamant demand is vacating Party-1 from the land. I request the experts to give the solution to the legal heirs get relieved from this problem and also to save the Party-1’s House from Party-2. I thank the experts in advance for the help.