Legal Question in Family Law in Maryland

If your father was mentally competent at the time he signed the poa, and was not under duress or undue influence from your sister, the poa would be valid. However, if he is still competent, he could revoke it at any time, and if you think he never intended to shut your mother out like this when he signed it, you should discuss this with him and encourage him to revoke it. Generally issue pertaining to health care are delegated by an advance medical directive that specifically discusses those issues and appoints someone, usually a spouse or child, to make those decisions if the individual is unable to do so. If you think your father is too incompetent at this juncture to understand what his status is and to sign legal documents, you would have to file a court petition for guardianship in order to overcome your sister's actions.