Richard J. Boudreau & Associates

Hello. I'm hoping someone can help me or give me direction.
In 2008 I co-signed for a loan for my nephew who was living with me at the time. Foolish, yes I know, but my heart was with good intention. Anyways, I received a letter from the above law firm stating that RBS Citizens have hired them to collect the money due. They called me here at work and my nephew was on the conference call as well. He was willing to make the payments, but they refused to deal with him since I am the co-signer and they are "within the law" to come to me for full collection. My nephew was adamant to them that this was his debt and not mine and that he wants to resolve the issue. They wouldn't go for it. Due to the fact I was at work, I had to hang up and the next day, a Brian Coyle called me and was very rude to me telling me that he is going to garnish my wages. He even asked for me to transfer him to our payroll department (which I didn't). I hung up on him as he was very rude to me.
Why would they not work with my nephew? Should we call RBS Citizens? I'm a single mom, I don't own my home, I work full time and I try to pay all of my bills. I was naive enough to co-sign on this loan, but my nephew wants to make good on it. I don't like being bullied. They told me that they have my employment verification and that garnishment is next. Can they do that? Doesn't that have to come from a court order?
I would appreciate any advice you can give.
Thank you for your time.