power of attorney/guardianship

He needs a Power of Attorney. Any attorney can do this but be aware the attorney will be representing your mother so do not get offended when he or she asks to speak to your mother alone to see if it is "OK" with her. Your mother must be competent to do this -- another issue that her attorney will have to evaluate.

If it is pretty clear she is not competent, then you are going to have to go to court to get a guardian appointed for her. Your dad may or may not be eligible to be her guardian. This will probably be fairly expensive. (In this case the attorney you consult with be your dad's counsel but the court will appoint an attorney to represent your mom so you are looking at paying the freight for at least two attorneys for several hours.)

In all events, get your dad to vest a power of attorney in you or one of your siblings so this scenario does not repeat itself if he has medical problems too.

As usual, this is just a general comment and not legal advice.