Do I have the right review mom's documents even though I'm not POA?

Read this.. It doesn't answer question but is informative
https://www.agingcare.com/articles/family-fights-over-power-of-attorney-153319.htm

Why do you feel you NEED to review the documents? I sense there are some issues of trust either between you and your brother or with your mother.

Quite the opposite, the POA is supposed to keep personal information confidential.

ive been poa and ive been carer without poa . i dont think sharing and being on the level with everyone can be anything but beneficial .
your statements back up each other . at some point if your words are consistant , people have no reason to distrust you .