Hi and welcome to HCM.
Your question is very unique and requires a unique treatment.
Treatment programs for individuals with fibromyalgia have been diverse and varied, and as yet no one single treatment has worked for every patient. Some patients have reported partial symptom relief with tricyclic drugs , while others have experienced success with traditional modalities such as heat and ice. Treatment through active stretching, postural education, body mechanics, and other forms of therapy has also provided some benefits. Specifically, it has become apparent that persons with fibromyalgia benefit from aerobic conditioning and other exercise programs. According to standards for fitness developed by the American Heart Association for a normal population, showed that 80% of patients with fibromyalgia are physically unfit.

For your brother it is important to start with simple , painless excercises , initially, by a method called Feldenkrais method.

In Feldenkrais method individuals perform small, gentle movement patterns, usually in a group setting, in response to verbal or written cues. The movements are self-directed and performed within each person's comfort range. Mental imagery of the movements is encouraged if the movements are perceived by the patient or the instructor to be too difficult. Mental imagery is also occasionally used as part of the lesson for all participants. Mental imagery has been widely studied and documented for its positive effects on learning. Also, the individual is guided hands-on by a Feldenkrais practitioner, who may be a physical therapist, through gentle and slow movements.

I hope this information is helpful to you.
Take care and have a nice day :)
Regards,
Dr. Nidhi Sood. (PT)