Sorry to hear about your cousin, yes definitely the nerve innervation in the polio affected limb are less, corresponding to less number of muscle fiber's being triggered at once Naturally, but if you can take your brother to a good physiotherapist in a good therapy center they might be able to help him recover by using FES (Functional electrical Stimulation) can be done wired or Wireless ( expensive equipment and more of a personalised equipment customized for each person). in the process the muscles would be stimulated by external means and strengthened. Hope this helps you.
Next Steps
Search a good Physiotherapeutic center OFFLINE and ask if they have F.E.S. and continue with the therapeutic services.
Health Tips
Don't mistrust the service because a goon of the service is not able to get result. it is because the person you hired does not have that knowledge. Acupuncture, yes they claim to increase strength but no significant research data to support the evidence, you can try at your own risk it might also help , may not. STAY HEALTHY.