Ancestral property

Sir, My uncle and his mother acted as head of their joint family of 2 younger brothers and sister( my mother) as their father died when he was 15 years and have sold some properties for the family purposes only with the oral consent of his brothers between1980 to 2001 without their signatures. This uncle has no children or wife as she passed away long back. He took care of his brothers' children. They partitioned the property orally . In 1991 this uncle and second uncle got pass book for their share. Third uncle never applied for the same. In 2001 my elder uncle sold one more property for my younger uncles cancer treatment. Third uncle died in 2007 without pass book. So first uncle got his land on his name and is ready to register to third uncles sons. Second uncle died a month back. No one is willing to take care of first uncle. He is kidney patient. The third uncles' children are forcibly trying to cultivate first uncles land along with third uncles land and are threatening of bringing some injunction order on his property and the sold properties. They are now 30 years old and uncle is 75 years old. He has pass book from 1991. How can he guard his share of land.