I understand how you must feel. Let me respond in two ways. First, is he on the proper dose of Ritalin and taking it throughout each day? It may be that his remaining hyperactivity, distractibility, and impulsivity are because the Ritalin is not being used in a way to reach maximum benefit. Second, it might be helpful to find a way to educate your relatives about ADHD.
If they will not listen to you, could the professional treating your son explain it to them. There are several good books that they might read (e.g., my book, etc.). I hope that with understanding they will be more supportive. If this does not work, stand strong and do what you know is best for your son.