I have been taking care of mom/dad's finances/bill pay for the last two years now. I have been added as a check signer so no issues with the bank, but I the Visa and a few others want POA on file in order to speak with me about the bill. Mom/Dad are 88 (suffered stroke recently)/89 (vascular dementia started) and both still competent enough and willing to give me the rights to help. All siblings are aware and on the same page.
In your case, you want to make sure your POA has durability language (i.e., a durable POA), since there will be a time when neither parent can make decisions on their own behalf and you don't want to be stuck with a worthless document.
Depending on your state, a "statutory POA" may be available (and there's usually a section regarding durability), or you may wish to consult with an elder law attorney to draft a POA for each of your parents and make sure the remainder of their estate plan is in order.
Best of luck...