I'm with Roger. I can't really see an instance where the government would ever want this.
Your parents are still, presumably, competent adults. Hence your father cannot decide such things for your mother. What is possible, though, is that you may have been asked to relinquish something during the separation proceedings, due to a conflict of interest. But a power of attorney would most likely not be such a situation -- I suspect that this isn't even a power of attorney at all (e. g. not a means for you to make medical and financial decisions for someone, should they become incompetent) but, rather, may have something to do with the property division.
In any event, if it's confusing us, I can only imagine how much it's confusing you. I am assuming (hoping!) that one or the other of your parents has legal representation due to the separation going on -- ask the lawyer what is happening and be prepared to pay for the answer, but at least you will know for certain.