URGENT!!! Can Durable Power of Attorney Agent in South Carolina prevent family members from visiting a critically ill brother legally?

No and yes, he specifically said that he wants no contact, yes. He is in danger from visits, yes. She decided that she now has the power, NO!

If this was my family member, I would call the local police and ask for a wellness check. Explain that you believe that he is being isolated against his will. They will speak with him and find out what is going on.

Be sure and ask the responding officer to tell your brother that you all want to see him.

Best of luck, these situations are so crummy.

I would contact Adult Protective Services and ask them to assist in an accompanied visit to a dying relative. Or ask for their guidance in how to arrange this last goodbye. I cannot guess at what sort of family interactions has resulted in an estrangement so severe that a POA would not want family visiting a dying person. However, we on Forum have heard from people who have estranged family showing up "at the end" for reasons that are not always good, so we likely cannot hazard a guess here. I would take the guidance of APS. A POA is charged with acting as directed by the person who appointed them while that person is competent and able to direct them, and acting in that persons "best interests" when that person is unable to make his or her own decisions. So in answer to your question, it is very likely that the POA does have, if this person cannot act for himself, the right (indeed the obligations) to act in his best interest.
I am so sorry. I hope you will be able to see your dying relative. If you are able to I hope you will leave outside the door any family trauma that is existant.

A PoA is responsible to make decisions in your brother's best interests. If your brother is not incapacitated mentally or physically then your brother might be having his PoA carry out his wishes. Or, if your brother is incapacitated his PoA is supposed to be making decisions in his best interests. Is it possible this power is being abused? Yes, but in order to call APS to report it you will need evidence of abuse. I'm sorry that this is unfolding in this way. Perhaps you can work through a family mediator to see if you can visit your brother.