An agent appointed under a durable power of attorney may not sign or revoke Wills using the power of attorney. However, a power of attorney may specifically authorize the agent to create, amend or revoke a living revocable trust on the person's behalf. (A living trust is an increasingly popular alternative to a Will as an estate planing vehicle.) However, the power of attorney must specifically address this particular power. Here's some of the language I include in my powers of attorney if the client wants to include this power:
"Create, Amend or Revoke Revocable Trust. I grant to my agent the power to create for me (and with my wife as to any property we own jointly) one or more revocable trusts (referred to as a "grantor trust") of which I am an income beneficiary and with such person or persons as my agent shall select as the trustee or co‑trustees, without bond or other security, and with such other terms and provisions as my agent shall deem appropriate…"
Without this specific authorization, the agent named in the power of attorney is out of luck on signing any estate planning documents for their parents.