How to get out of a fake acquisition on property fraud

my late grandfather has 2 sons and 3 daughters. my dad, the elder son, has 3 daughters and my uncle has a son. uncle has always been irresponsible and been running away from home since teenage and does not stay with his wife and son even so my grandfather gave his will to my dad and uncle's son on the ground that uncle is mentally unsound and irresponsible. now my dad's cousins are brainwashing my uncle and he has complained against my dad that he is not giving his share in property and can harm him rather i am afraid that they might harm him and blame my dad because they want to acquire our ancestral property please tell a way how to proceed legally?