Final answer:
The nurse should prioritize patient confidentiality and privacy when dealing with a family member who is physically abusive and demands information about the client's treatment. They should inform the family member that personal information cannot be released without the client's consent, while encouraging support and direct communication with the client.
Step-by-step explanation:
When the allegedly abusive family member calls the unit and demands information about the client's treatment, the nurse's best response is to prioritize patient confidentiality and privacy. The nurse should inform the family member that they are unable to release any personal information about the client without their explicit consent, as this would be a violation of privacy laws. However, the nurse can encourage the family member to provide support and communicate with the client directly, without disclosing any specific treatment details.