Will the estate go to my mother or to the power of attorney?

The power of attorney does not survive your father.

You're correct. When your father died, his Power of Attorney ceased immediately and the only thing left is his Will. However, your mother has what's known as a "Right of Election" which she can assert in the event that she was not mentioned in your father's Will. In such a case, it will depend upon how many children exist at to how much she gets under her Right of Election. If the Will otherwise says the house must be sold, there are a number of other issues that could arise. I strongly suggest your mother consult with a local estate attorney and you and your brother go along to find out what the law dictates in these situations. Unless your father was at odds with your mother at the time he made out the Will, I would be surprised if he was the only owner of the property and that he would direct the sale of the house while she was still alive. Instead, I suspect she may either get the house by operation of law if the two of them owned it together or she will get a life estate in the house to allow her to live out her life in that house. Those would be fairly normal ways attorneys would suggest when making a Will for someone. Good luck.