How can I get property of my father

My father was purchased 4.5 acres of agricultural land. He was died in 1998. After that the property named with my mother. We r two brothers n two sisters. I'm last son in my family. All the documents of property r with my brother. Recently I had a clash with my brother in some money matter which was included some man handling . Now we both were not talking with each other. Recently I was asked copies of that property doccuments.He taken this as an opportunity and blackmailing me that I don't have that property documents. Pls help me what I have to do????