I'm Doug, and I'm very sorry to hear of your situation. My goal is to provide you with excellent service today.
Only a court can make an order appointing you as your father's Legal Guardian. If your father is unable to care for his own affairs, or even if he is borderline and agrees to have to act on his behalf, the court will grant you guardianship.
Guardianship are not automatic though and your father would be best served by you obtaining a local Probate Law attorney near where he is residing to apply for the Legal Guardianship.
On a side note, if his social security check is deposited into a joint bank account with his wife, it is important that you get him to the bank to open a separate account so his wife can't steal his money (nut don't close that account yet) and take him to the local social security office to help him notify social security of the new account number for his direct deposit.
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I wish you and yours the best in 2016,