Hello I am a solicitor with 20 years experience. I will try to help you with this.
OK the bailiffs can only take property belonging to your nephew. They can not take property belonging to you. You should contact them and tell them that your nephew does not live at your address, never has done and (I assume this is true) none of his property is at your address. If you know his address you might tell them and you should certainly let your nephew know about the bailiffs who are pursuing him, so he can contact them and sort it out.