Can DPOA be changed after incapacitated?

Pam is right. A person has to have good credit to become a guardian. It sounds like your brother would be their last choice for the job. If he applies, be sure to write a letter to the court detailing all that has gone on. It sounds like he wants guardianship so he can have access to their money for himself. That is not allowed, though sometimes the court can allow small amounts of money for pay. The thing I would be worried about is that the court may appoint someone outside the family as guardian if your brother does this.

Brother sounds like a total a$$. It's a pain to have family like this when things are already stressful enough.

Judges don't award Guardianship to people who use their parents' credit cards for their own benefit. Nor do they trust someone with bad credit. Your DPOA is valid until a Judge says otherwise. Pull out the records of his financial abuse and present them in court. He's going to look really stupid and even criminal, depending on how much he took.