Let's see if we can try and save you some money here and a bit of effort as well. Correct me if I am wrong at any point
You have two macs, two telephone lines and three bills
Cancel one of the telephone lines,
Buy a router, you would then be able to connect the existing hub to the router.
You would only need one static IP address which would be assigned to the router and the DHCP would assign dynamic IP addresses to the MACs.
You may not need to buy any modems as many of the ADSL broadband routers have a built in ADSL modem,
A microfilter is a small device that plugs into your normal BT telephone socket and splits the line into both a standard BT telephone socket and a ADSL broadband socket
Please post your query to the boards as many hands make light work, and I'm not talking electricians! If your problem is solved, let us know so that others can learn.