Can a sibling of mine get me revoked as POA?

a. If you are the agent for your sibling under power of attorney, then that sibling, if they have requisite capacity, can generally revoke your authority as agent under that power of attorney. In that case, your sibling would be what's known as the "principle" under that power of attorney, and you would be there "agent." Generally, most power of attorneys are revokable at the discretion of the principal. 

b. However, if you are the agent for someone else (other than your sibling) under a power of attorney (such as for one or both of your parents), then generally your sibling would not be able to provoke your authority as agent under the power of attorney, as they are not the principal. The principal under the power of attorney is generally the only person who can revoke the power of attorney (or the Court in some circumstances). But all powers of attorneys are not the same. To give a precise answer, I would need to read the specific power of attorney in question.