The parents of the children have the sole duty and authority (outside of a court order to the contrary or an emergency) to provide medical care for their children. A doctor is not going to provide treatment without one of their consent. If your brother (I am assuming the children's father) schedules the medical care because he deems them appropriate, then there is no legal remedy for the mother against you. You would simply be the one transporting them to the appointments authorized by their father.
Responding to questions on AVVO does not establish an attorney-client relationship between the questioner and any attorney associated with Garrett Law Group, PLC. Responses should be considered and used for informational purposes only. Every case is unique in its facts, and all legal matters should be discussed with a licensed attorney prior to making any decisions or taking any actions.
The purpose of this site is to offer general information and NOT legal advice. No lawyer can give legal advice without hearing all of the facts. Based upon the limited information you have provided the immediate answer to your question is no, absent a power of attorney, court order or written authorization signed by both parents. If the parents share joint legal custody, most professionals will not treat the childern without the consent of the other parent. By law, if the parents share joint legal custody, each parent must confer and consult with the other before making any major decisions. If the father seeks treatment and the mother is withholding consent contrary to the best interest of the children, based upon the facts, this may constitute a material change in circumstances. If so, it may warrant a possible change in the exiting order. In order to protect the well-being of the children, your brother should consult with an experienced family lawyer in the area. If the interest of the children is being compromised, the court can get involved, once a motion is filed with the court. Best of luck to your family~
This response is only intended for informational purposes and is not intended as legal advice or as a substitute for hiring an attorney in your state. Further, by sharing this information, it is in no way intended to establish an attorney client relationship with the reader.
Sign up to receive a 5-part series of useful information and advice about child custody law.