Site problem

Hello All, 1. We have purchased site in the year 2008 from X person right we are owner of site. 2. X person got site from her father (let's consider Y) with sale deed in the year 2006. 3. Her father (Y) got site from (Z ) person in the year 1993 with GPA. 4. Z has person got land owner let's consider (P) in the year 1990 with GPA. in the year 1990 no where registration hence they have made with GPA. NOW case booked with P (sons) Vs X. ( Land owner sons claming that, this land is not in the name of our farther... it is with our mother. the total land is 4 acr 30 gunte her mother got this land with her parents.. sites are made in the year 1989 only. ) The P sons done registration on Nov 2014 by his mother as gift deed and same site sale in the Dec 2014 one more person they are not booked case against with us since our father is in Police Dept. they booked against were we purchased from X. and more over they bokked only open site almost 7 - 8 member same like us in bangalore rural court. Pl note the land is not a DCconversion land in the year 1990. now it's come under BBMP B khata. We have checked all the govt doc. the doc not availble in the kandaya BHAVAN also. we have xerox copy in the Phani in the name (P) he is land owner We have paid year to year tax paid recipt. Now they have one shot tax paid receeipt in the same day. We have PID no. they don't have ( we are in position construted small house and given for rent, current bill coming with our name) . they called several times for comparmise but we refused. PL can any adovacate guide how to go us. thanks in advance your valuable inputs .