The legality of your brother making a claim for the house would depend on various factors, including the laws of the specific jurisdiction where the house is located and the specific details of your mother's estate planning.
If your mother granted you power of attorney, it means you have been given the legal authority to act on her behalf in financial and legal matters while she is alive. However, this authority typically ends upon her death. At that point, the last will and testament become relevant.
If your mother's last will and testament clearly states that she has bequeathed the house to you, and it was executed properly according to the laws of the relevant jurisdiction, you should have a legal right to the property. Your mother's will should specify her wishes regarding the distribution of her assets after her death, and as long as the will is valid, it should be followed according to local laws.
If your brother believes that the will is invalid or that there was undue influence, fraud, or lack of capacity when the will was created, he may challenge it in court. This is commonly referred to as contesting a will. Contesting a will is a complex legal matter, and your brother would likely need to provide substantial evidence to support his claim.
It is important to consult with a qualified estate planning attorney to understand the specific laws in your jurisdiction and to get advice on how to handle any potential disputes or challenges to your mother's last will and testament. Estate laws can vary significantly from one location to another, so it's essential to seek legal guidance tailored to your situation.