If the person is legally incompetent, you will need to obtain a guardianship along with a medical examination of the person you are trying to get powers over and have it approved by the court. If the person is competent, he/she would execute a Power of Attorney and sign attesting that he/she is legally competent. If other parties know that this person has dementia, the Power of Attorney may be challenged if they believe that the person signed while not legally competent.
If the person is legally incompetent, you will need to obtain a guardianship along with a medical examination of the person you are trying to get powers over and have it approved by the court. If the person is competent, he/she would execute a Power of Attorney and sign attesting that he/she is legally competent. If other parties know that this person has dementia, the Power of Attorney may be challenged if they believe that the person signed while not legally competent.
