I'll weigh in here, as we had this issue with my mother-in-law many years ago. She too entered the nursing home voluntarily while battling glioblastoma, but was totally aware of her situation. She wanted to be full code, and signed papers to that effect. I was handling her finances, but was not her medical power of attorney, and a finance person asked me the same. Needless to say, I was appalled. I reported the situation to the facility administrator, who reprimanded her and apologized to me. 10 years ago, my daughter was the RN Case Manager in the assisted living facility where my mother resided. Their policy was to address this matter only during a case conference with the resident and their legally named representatives. And management and administration were the only ones authorized to do it. In your situation, knowing your Dad's wishes as you do, I would report the matter to the Administrator or Director of the facility.
Sue