H.M.
If she has power of attorney you would have to get a lawyer possibly. If he is cohirent enough talk to him. If she does not have power of attorney over him I would say you are still next of kin and could contest it. You stil may have to get a lawer for that. I would talk to the nursing home as well so they can be made aware of the situation and they may even be able to help you.
Good luck and God Bless!