My cousin is threatening my father for money what can we do

A person is disturbing our family a lot. He is my cousin, that person is the son of my father's brother .my uncle is dead .after his death my father take care of his family .his mother is a cheap person .my father gave him the whole house of villege and lots of land without any condition because they were irritate him a lot. My father is a govermented employ.by wrongly he accepted that the person is his child on stamp paper .but there is many stamp we have in which it is written that after taking that lands they will never contact us.but recently he again threaten my father.what will we do next .please suggest us quickly ,we are in very danger.