You may want to look toward filing a petition for guardianship under chapter 744, Florida Statutes. This would allow you to make decisions regarding your father's affairs.
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You are now past the point of a power of attorney. Now you should file for guardianship. A family lawyer can help you.
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I agree with the previous two attorneys. You are past that point where you could obtain your father's signature on a Durable Power of Attorney. However, one glimmer of hope, you said that your dad is in a medically induced coma. Will he come out of it? If he does, will he be competent to sign. Even if he cannot sign, someone can sign for him in his presence with his permission if the notary is present at the same time -- as long as he is competent.
If you can avoid a guardianship, by all means, try to. They are very vexing and expensive in Florida. That's why everyone over a certain age should have a durable power of attorney.
The foregoing is not intended as legal advice or to create an attorney-client relationship. Such Legal Information is intended for general informational purposes only and should be used only as a starting point for addressing your legal issues. It is not a substitute for an in-person or telephone consultation with an attorney licensed to practice in your jurisdiction about your specific legal issue, and you should not rely upon such Legal Information.