Ah! If you can mount the WiFi unit in the attic on its side, so that the antenna is horizontal, then it will "squirt" downwards into the rooms below.
If the antenna is vertical, the signal comes off it horizontally (mostly).
Meanwhile, the telephone...
Connect the two available wires for telephone to pins 2 and 5 in the master socket. That doesn't pick up the separate "ring" line. If you want the added one to ring, then buy a "master" socket to go on the end of those two wires.