Been there, done that. Now, listen carefully:
Unfortunately I didn't get it quite right!!! Try again:-
Your wireless router can connect to T-online for both of you. In the router parameters, set "internet connection type" to "PPPoE". Set username to "AAAAAAAAAAAATTTTTTTTTTTT#MMMM@t-online.de" where "AAA..." is your Anschlusskennung, "TTT..." is your t-online number, and "MMMM" is 0001. Set "password" to your Zugangskennwort. Also set "keep alive".
Your email programs need to use a different server than before:
mail in: use "pop-mail.t-online.de" on port 110, username="TTTTTTTTTTTT-0001" or "TTTTTTTTTTTT-0002"
mail out: use "mailto.t-online.de" on port 25, username="TTTTTTTTTTTT-0001" or "TTTTTTTTTTTT-0002"
For the 0002 user, you will have to set a password on the server: go to the t-online site and follow links to Service" - "Mitbenutzer" - "Verwalten".
Violá.
The lovely thing about this is you can throw all your t-online software away!