There is no legal requirement that would give a person, even a close relative like you, the automatic right to review a power of attorney in which you are not
But in reality, that's probably not what you really want, anyway. It sounds as if you have some nagging doubts about whether your brother is acting on the up and up, and some fears that he may be squeezing you out of the picture in some way"”and all the reviewing in the world wouldn't change that. About 99% of the powers of attorney for finances read the same way, anyway"”just enabling the agent to manage money for another person's best interests while he or she is alive.
It sounds as if it's that "best interest" part that you and your brother need to get straight between you"”and maybe, just maybe, that will be a little easier given that the two of you have had a good relationship in the past.
If you haven't done so yet, sit down with your brother and have a very focused and frank conversation. If you've tried this already, try it again. Explain that you realize that you and he want the same thing: to keep your mother as happy as possible and to avoid problems in the future. Without accusing, ask him to explain why he needed the power of attorney at this time; it might be something as simple as needing to write a check or transfer your mother's money between accounts.
Once you are living in your mom's home, the reality is that you and he will likely have to work together more closely in handling your mom's finances. So perhaps you could agree to be transparent with him by keeping a running log of her daily expenses if he will do the same for you with her home expenses that he is managing.
If this transparency idea doesn't work, there may be a legal solution: You could go to court and ask the court to require your brother to file a periodic accounting. While most courts will agree to require this, you can see that it can often have the effect of creating bad blood between the siblings involved. So probably better to try the informal approach"”at least at first.
Finally, the issue of what will happen with your mom's house seemed to come up a few times, at least between the lines of your question. So that is another issue you and your brother will want resolved. Find out how the title to the home is held"”and whether your mother has a will or trust that leaves it to others, as that may play a part in the complete picture.
Listen and convey the feelings involved in all this, too. If your brother is a straight numbers man, for example, he may not be aware that your mom's house provides her with a great deal of comfort. He may not be aware that getting her some supplemental in-home care if needed may be less expensive than moving her to a facility. He may even feel that since you're moving into the house, he needs to protect any interest he may have in it. Find out.