Ancestor property

We have an ancestor’s property which was given to us during British period. Through a title deed we own the property. It’s in the name of my great grandfather’s brother. It is an undivided property since they lived in a joint family. The said title owner was maintaining the property though he was not the eldest. My great grandfather was the eldest along with 3 brothers and one sister. Recently, after the death of my father three years back I came to know about this property. The above mentioned brother of my great grandfather had no children. He has adopted a son and he started enjoying the entire rights of the property with his brothers and sisters. Since there was no family settlement done, my father (when he was alive) approached them so many times and was insulted. Now it is being sold to people without the consent of the other title holders i.e., the brothers and sister of my great grandfather. I am the second son of my father. Do I have any ‘say’ in this regard..? and how do I take legal action against them..?