Undivided land sold by co-owner

My uncle sold his undivided share to outsider without our knowledge or signature, he sold total 1 Karnal land in verious almost 10 khasara numbers. am and my brother not want to sold our parental land to any outsider, now those purchaser file a suit in tehsildar office for partition. Request to you please help me on this. how can i got back those land. in those number most of the land are agriculture land which are cultivated by me.