POA and Guardianship Question -- HELP!

When my mother did durable poa with me, she was the primary caregiver for my father so the document indicates wishes for both her and my father but she signed it, not my father who was not capable of signing off......after a recent tragic accident, she is now incapacitated. Does this poa cover both my mother and father?? or just my mother since she was the only parent who signed it?? I'm asking because my sibling is threatening to apply for guardianship of both parents and I don't think that's possible since the poa exists BUT does it apply to both parents?? Can she still obtain guardianship of either parent or both??