Land encroaching by a land mafia on basis of false claim of being owner of land.

First owner of land registered her land to 2nd ,2nd sold it somehow to 3rd person (in 1996) but in detail it shows that "3rd person is on owner of the land by a settlement" ,i.e, "samjhaute k Aadhar pe 2nd ka Naam hata k 3rd ka Naam darj Kiya jata hai " and third owner registered the same land to 4th and 4th registered the land to my father ,he is 5th owner. Now,in 2015 a land mafia claims that he has purchased the land , actually,he. Took registry from the sons of owner number 2 and said that...Thier father never registered that land to anyone so it belongs to them and now they sold it to land mafia ,so it belongs to him. My father has sold the land in parts to nearly 18 customers and few part is left in it,and my father and 18 more are thrown out of their land because the land is named to land mafia and he is encroaching the land . Can we get our land back ? If we did not do anything wrong,why are we being punished ? Number 3 did not took registry but still he sold it and we took registry even though we are thrown.