if one sibling has POA and there are 10 other siblings. Do we have the right to see a copy of the POA?

You probably don't have the right. Mom made a decision that apparently doesn't involve you. There's a good chance you already know why this has occurred. If the sibling won't tell you, will mom?

It's always better to appoint a person who can spell as the POA. Bear in mind the form has many big, long words that only lawyers understand. Find a lawyer who can explain how that works.