Bell boxes. The thing that goes ding dong!
That changes things, mine uses 8Ω speakers, with the ding dong type they even overload a standard transformer with one bell, it relies on the user not holding his finger on the bell push, if all the same rated at 8 volt then using a 24 volt supply and wired in series would work, the bells are only a coil of wire there is no contact in them to make then ring.
However that means getting a 24 VA transformer, in fact does not matter is 8 volt or 24 volt, still need a 24 VA transformer and most bell transformers are rated 8 VA. I did look
found these at £51.54 plus vat trade. The point of course as soon as you start to look at modifying then one has to ask what about a 3 volt DC power supply to a wireless unit?
I tried these
it seemed great, it seems at first glance that
this version would do you. However having tried to use it with a DECT phone it seems with a standard phone the door bell is registered as one phone so pushing door push is like ringing an internal phone, and you have to set which of the three phones it rings, which is not what you want.
So before buying give them a ring and ask if pressing door bell rings all three phones, it may be the phones in the kit are not the same as standard DECT phone, it may ring all three, but check.
The idea was my mother could answer the door bell and find who was there before she transferred into her wheel chair and went to door, so she did not need to answer the door to those religious hawkers. However she never got the hang of it. But where the bells need to be spread around the house then we should expect it to take some time to answer the door, so talking to people at door before answering does seem to be a good idea.
Do a hunt for door entry systems rather than door bells and you may find what you want.