If you have a ADSL? four wire telephone cable connected to the outside of the house at a junction box and two of those four wires are connected to two of the eight wire Internet cable (that leads to the modem), can you also run a external 8 wire Internet cable off the junction box 8 wire connection to run a long distance (30m external) cable from the LAN off the modem, to run another computer junction in another building?

The problem I face is I don’t know if the two wires that are being used to hard wire the telephone cable to the internet cable leading into the modem can also be used at the same time to export say the information out of the modem LAN through the Internet cable to the new building so to use the internet.

Or I need run a new 8 wire cable directly from shed to house into the modem outlet port.

Two pictures one shows the new added Internet cable and the second image shows that I temporarily broke off the connectors to rejoin the telephone cable and shows the new Internet cable that I want to join the eight wires to.