Right of Elder Son and on Fathers Property

My Grand Father has left Property with out any written WILL and has 2 sons, my Uncle (younger Brother of my Father) has died before my Grandfather and also my Grandmother. My father is elder Son to my Grand father and we are 2 sons. My uncle has 2 kids (one Son and Daughter). The property is on my Grand fathers name but it was my Father and Grand father who has worked to gether and developed the property (All the Income earned was together). My Uncle didn't had any stable income and a business started by my father was given to his brother (my uncle) which he didn't run sucessfully and closed later. After my Uncle's and Grand Father's death my father took care of my 2 counsins and my Aunt. We also performed my Cousin Sister's marriage. My younger brother is Physically challenged and due to family circumstances my father kept all his / spent all his income to the developement and well being of the Joint family. Though my Grand Father didn't didn't left any written WILL, but when he was alive he always said that 3 Grand Sons will have equal share on this Property and was been said to some of his close friends and family friends. Due to differences my Cousin brother we want to partion / transfer the property, what will be our right? Whether we can claim to make property into 4 partitions - 1 each for 3 Grand sons and 1 part for my father (Elder Son)? As my younger brother is Physically challenged, will he get any special rights on the property?Please advice. Thanks in Advance