Dispute in ancestral property

Hello sir my name is ankita.this property is of my grandfather who died when my father was 2 year old.my father are three brother, my father is younger. first older brother died.older brother's sons have the registry of house.my father is very polite and simple person...older brother's sons take advantage of my father politness and they harras in every aspect. they dont want to give the portion of property..as thier father and my father prepared the document and map..but before my big father sign those paper he died. i dont what to ask , i am in depression because of them..they harrased me and my younger sister ..they are very cruel..how can i save my mother father, my family from them...we want the separete from them...tell me the process of distribution...do i need their son's signature for different registry.any other process i can easily separate the property.because they never said clear no..that they wont give original registry of house.but they never gave registry..what to do....please help me...