Property dispute

Dear sir / madam,

My Grand Mother has four daughters and one son (who is mentally challenged) and she has expired in 1986 but she has not done any will.  Now only two daughters and one son is there.  who will have the right on grannd mother property.  One younger daughter is living in her mother's house and taking care about his brother who is mentally challenged.  Rest other daughters are well settled and no body is taking care about the brother.  kindly inform rights about this property.