If there is a dual jointly acting POA and one representative was NEVER consulted for anything what do we do?

My Grandmother has been severely abused by one jointly acting POA where the oldest sibling was never contacted by the courts, hospitals, banks, social services and many others that had a copy but didn't follow. What can be done? These severely disturbing actions could have been prevented and in turn, the abuse! And it could have been stopped! The courts we have recorded even stating they open and closed the case with all evidence submitted. Three months later the DA's office confirmed the evidence wasn't submitted even though we have it recorded that it was! Now that we find the original POA accidently sent by abuser we need help for it's not being followed as it was to be in order to prevent what has happened!