Alzheimer's and Advance Directives: Figuring out Dad's Wishes

HOW DO YOU GET SOMEONE WITH ALZHEIMER'S TO FILL OUT ADVANCE DIRECTIVES? - "I am having a difficult time trying to get my dad to fill out his advance directives. He cannot focus on the questions. He is living with me because has early Alzheimer's and was not making it on his own. It would be best if I had a Power of Attorney to manage Dad's financial affairs. While he has no money, he does have medical bills and other expenses to manage. He needs his advance directives completed. How do I get this accomplished?" - READER