[Dave Moll]

The only simple way to eliminate the bell tinkle on the other 'phone is to have the two bells connected in parallel (hence the third wire). When dialling, the local bell is shorted out by contacts in the dial that are activated whenever the dial is in a position other than at rest (the dial-off-normal contacts). Unless the remote bell is connected via the third wire to these contacts, it isn't shorted out and will tinkle as the DC line current is alternately increased and decreased by the loop-disconnect dialling - looking somewhat like the AC ringing current used to sound the bells on an incoming call.

You say that you have additional wires available in the wiring between your sockets. If you connect your internal wiring to the output of your ADSL filter (including the third wire) this should solve your problem. Do not use any further filters on your extension sockets. You can then, if you wish to keep ADSL separate from the 'phones, use a separate pair to a socket for your router.