Can someone explain wage garnishment laws here?

Child support and unpaid taxes are subject to wage garnishment in all states I'm pretty sure. But some states such as our home one of North Carolina limit it generally to that, garnishments for basic credit card debts for example aren't supported by state laws. Now what about a private (non federal) student loan? I'm trying to help my brother pay off his loan from college (I was his co-signer) but we're both tapped and so are our parents, so it may go into default. Sallie Mae isn't willing to work out anything more with him. Are our family's wages now subject to garnishment? Or wil it just toast our credit scores? The latter we can rebuild, we'll have a larger income eventually so we can take care of that. But right now we don't have extra money to give away, if we did we'd just make the monthly payments. So to recap, how would the state of North Carolina treat this case?