POA Rights and Responsibilities?

When my parents divorced 15 years ago my brother paid out my father's share so that my mother could stay in the family home. To be honest my mother didn't need his assistance and my other 2 siblings and myself were more than happy to chip in to help her. In the last few years I have found out that my mother signed over the property to my brother and he went on to building another house on the back of the property and then sold the front house which was to help my mother be mortgage free.

Years have gone by and my mother is living in the newly built house which still does not have a building of compliance and this has been going on now for over 10 years. The house is not even in my mother's name it's in my brother's name and I have just found out a couple days ago that my brother has now put the house into a trust, his family trust.

My brother is robbing my mother of her independence which was the promise from the beginning and also robbing myself and my other two siblings of our inheritance. Where is the justice in this? My mother worked hard to have her own home and now my brother sees it as his right to take it.

What can my siblings and I do? I believe he is her POA. At the time she signed over her rights to the property she was mentally unwell because my father left her for another woman and 15 years on she still is not 100%. I believe she had a mental breakdown at the time and my brother took advantage of the situation.