The man started the conversation saying that his father had signed the Medical Power of Attorney several years ago. His father now wanted to revoke it and appoint a new agent for his mother.
Do you see the problem?
The man had printed out a Power of Attorney form he found online several years ago. He and his father thought it was acceptable to appoint an agent to make medical decisions for his mother even though his mother was incapacitated and did not direct them to sign the Power of Attorney.
The Texas statutes specify that you should sign a Medical Power of Attorney in the presence of two witnesses or before a notary public. If you are physically unable to sign, another person can sign for you in your presence and at your express direction.
No one can sign a Medical Power of Attorney on your behalf otherwise.