Are all PMR radios compatible?

Yes, all PMR radio devices are in principle compatible with each other, provided they adhere to the specified PMR446 standards, which apply in Europe for license-free radio communication in the 446 MHz frequency range. They can work on the same channels and with the same subtone codes (CTCSS/DCS), which means that devices from different manufacturers can communicate with each other as long as they are set to the same channel and subtone.