No, it is not legal. Being a legal guardian is not a legal delegatable duty: that is, it is not a duty or obligation which the legal guardan can pass on to any other person, including his or her agent or attorney-in-fact under a power of attorney. The agent cannot act as the guardian over the incapacitated person. If the legal guardian no longer wishes to be guardian, is not available due to moving or other obligations to exercise this responsibility, and/or is him/herself not incompetent, a new guardan must be appointed by family court.