How can I prevent my brother from taking mother's property share?

My father willed his self-earned property to my mother in 2005 (he died of cancer). My mother has battled schizophrenia since 1993, and my wife and I have been taking care of her for over 21 years. My brother kicked her out of his house in 2010, and since then, he has not taken care of her. After this, my wife and I have continued to care for her. Our jobs have been compromised due to the extreme care my mother requires. My mother transferred her share to me and wants to give my brother’s portion to me. She does not want my brother to receive a single inch of this property. I have nothing else to sell in case I need money in the future. How can I stop him from taking away this portion from us?