Check if the usb adsl modem
has the RJ45 interface, if not, the easy way to share internet is by changing the u***** ADSL Modem to a RJ45 ADSL modem. The u***** one is getting obsolete and is a very stupid product IMO.
Then the connection will be:
Telephone line ---> ADSL Modem ---> Router ---> Computer one
|
---> Computer Two
(Most of the connecttions are through RJ45 ports)