Final answer:
The patient should have a family member present when explaining hearing instrument use and expectations in order to address any misunderstandings and ensure proper usage.
Step-by-step explanation:
When a patient returns after only a week of wearing their new hearing instrument and complains that they are not hearing much better and experiencing constant whistling, it is important to investigate the issue and provide appropriate guidance. In this case, option C is the most suitable solution. Having a family member present when explaining hearing instrument use and expectations can help address any misunderstandings and ensure proper usage. This way, the patient's family will gain a better understanding of the device and can provide support and assistance if needed.