You used to be able to get a USB router that took the USB output from your modem but this was discontinued
http://www.draytek.co.uk/products/vigor2200usb.html . Perhaps there are other USB routers about.
You could replace the supplied ADSL modems with a combined ADSL modem/router. There are many about but never having an ADSL connection with more than one PC I have no experience with them. A couple are mentioned in the link I just provided.
This thread needs moving to the correct forum are as it is not a NTL broadband issue.