If your brother feels his lawyer didn't represent him appropriately and engage in an ethical violation the first step is to report him to the appropriate disciplinary organization. Follow this link to file a complaint in Ohio. http://www.supremecourt.ohio.gov/DisciplinarySys/odc/complaint.asp
You can sue a lawyer for legal malpractice if you feel his handling of the lawsuit was below the standard of care applicable to the lawyers in the community in that field. However, it is not easy to prevail on a legal malpractice lawsuit. Just because you feel your lawyer was not as diligent as he should have been or did not do everything he should have done, does not mean you have a viable legal malpractice claim. In order to prevail, you have to show not only that the lawyer's conduct was below the standard of care but also that you were damaged by it. If you would have ended up with the same result even if the lawyer had acted differently, you have no damages. You should consult a legal malpractice lawyer in your state.
This response is for information purpose only and does not constitute a legal advice. This response does not create an attorney-client relationship.