OK, so you apparently want to detect the chime tones and mirror them to another station by wireless rather than properly wiring them. I would note that you can get flat cable to run under carpets, skirtings or wallpaper, even paint.
The chime signal here is an audio signal with a variable volume, it is not going to be entirely easy to reliably detect and it is not referenced to either side of the transformer AC as that is passed through a bridge rectifier.
In any case, you are going to need a number of components but I suspect the easiest will be to forget Arduinos (despite the common meme that an Arduino is the solution to every problem ) and connect a "Video sender" (using the audio only) with its own power supply to the door phone master unit (are there actually any slaves connected?) and a "video receiver" with a small amplified speaker where you wish to hear the chimes.
If you are particularly clever, you could probably use an isolation transformer at the master phone to obtain power for the video sender (or whatever other system you devise to detect the chimes).