Will guardianship over my mother override the Power of Attorney her husband has?

In short, my mother was in a rehab center 2 1/2 yrs ago and was being moved to long term care for dementia. Her "friend" (now husband) told her "if you marry me I will take you home". Hence , they allowed the marriage to take place in the nursing facility and he also had her sign power of attorney over to him. She is now in a nursing facility due to end stage alzheimers. I am applying for guardianship of her because he is threatening to take her out. This is against all professional's advice that we have dealt with. I have the physician's certification from her doctor and I am reaching out to another (as I need 2). If approved by the court, will this guardianship trump his power of attorney. He is not capable of caring for her, he removed her in April and 5 days later, I had to have her admitted back throught the ER, and then re-admitted to the nursing home. Also, he is refusing to give any of the 3 daughters her late husband's (their fathers) urn, and her personal belongings. Thank you so much for any information or insight you can provide and thank you for taking the time to read this. I am in a real dilemma, as soon as I receive the 2nd physician's certification I will be filing the guardianship papers with the Surrogates Office / Court. Thank you