If a parent appoints a son to be POA over the mother and the father dies is the POA legal?

Yes, the Power of Attorney (POA) remains legal even after the death of the father, as the authority granted to the son pertains to the mother, not the father. However, the son can only act on behalf of the mother in accordance with the terms of the POA. If the mother passes away, the POA becomes void. It's important to ensure that the POA complies with relevant laws and requirements in the jurisdiction where it was created.