My late mother's property . What proofs required to lodge a case

My mother passed away when I was 4 year kid.my father passed away before 7 years. And my grand mother passed away a year ago. My mother's elder sister's are selling and taking the property.i have 2 younger siblings. How can I legally lodge case for this property.i do not have any govt documents like mother/father death certificate, marriage certificate nor our birth certificates