You should not be posting incriminating information on public sites. Retain a criminal defense attorney with expertise in DUI cases. You may qualify for a first time offenders program known as ARD. Under this program you avoid a conviction and incarceration. Good luck.
If your company has a policy concerning drinking on the job you can bring that information to management. Additionally, you can confront him and let him know of your concerns. If he just pled guilty, he probably has a probation officer monitoring his case. Drinking and driving would be a violation which would result in him being incarcerated. If all else fails, if you see him drinking and driving, call the police.
Your heart is in the right place, however, the only thing that will help is the best representation possible. Since your nephew already has an attorney, it would be inappropriate for another attorney to provide an on line opinion. If your nephew is not happy with his attorney and if he or his family has the money, then a criminal defense attorney with expertise in homicide cases should be retained.
Sounds like you lost confidence in your second lawyer. If this is your first DUI you are not entitled to a jury trial. It is suggested that you attempt to resolve the conflict you have and if you can't, then hire a third. Good luck.