Aiden, as a retired Telephone engineer I can tell you it was quite normal to hear each party on a shared line, it often caused friction. Also when work was carried out on the cable, if the line got "reversed" when you dialled the one party it rang the other, and when one party made a call it registered on the others exchange meter - more friction!!!! its only advantage was a lower line rental. They were slowly phased phased out as more cables were laid. Could have been worse, in some parts of rural America they had up to ten parties sharing one line !!! Eric