Must I revoke the general power of attorney granted to me by my parents, especially given my fear of my brother's actions towards their properties, and would my evasion of revoking the power of attorney be considered an act of disobedience?

You must obey your parents and cancel the power of attorney, for your disobedience to them in this matter is a forbidden act of undutifulness. The power of attorney is legally invalidated as soon as they dismiss you, and this does not depend on official procedures. If you act according to the power of attorney after knowing of your dismissal, your action is void. You must cancel the power of attorney in official departments and be dutiful to your parents, and advise your brother to be dutiful to his parents. Your parents have the right to dispose of their property by sale or gift, but the preponderant opinion is that a gift to children must be equally distributed among them, unless there is a need.