Not so out-of-the-ordinary, and we will be able to help.
You mentioned the PMR446 radios, which makes us think you are probably in the U.K. Is this correct?
PMR446 radios are similar to the GMRS/FRS radios we have here in the U.S. and Canada. You even have access to some high-end PMR446 radios that we can’t get here, but it seems like the Motorola T92 radios in a PMR446 configuration will work well for you.
Here are a couple of things to understand about two-way radios in general:
#1 - No UHF radio can violate the laws of physics. They are strictly line-of-sight, meaning they will only reliably transmit and receive a distance of a few blocks, regardless of how they are advertised.
#2 - The Motorola T92 is at the high end of consumer-grade radios. They are designed for families to communicate with each other; they are not designed for critical public safety applications. If you are good with that, they will meet your needs. Just be aware that they will not have the lifespan of professional radios, and usually the batteries, charging connectors or headset connectors start to fail after a year or so of hard use.
#3 - PMR446 is a publicly-shared frequency spectrum, and NOTHING you say will be 100% private. GMRS/FRS and PMR446 radios have tones that one can set that will only open the squelch if the calling radio transmits the same tone as the receiving radio, but you are still sharing one public channel. Anyone with the same tone can listen and transmit, and anyone with no tones set can listen to everything you say.
Now the good news. Our forum hosts carry the Ritron series of two-way radio call boxes. They are great quality, and Ritron makes both analog and digital variations. They CAN be programmed for GMRS or FRS here in North America, or PMR446 in Europe. (You want the analog version, with UHF frequency range 450-470 MHz.)
The Motorola radios don’t need programming, but the Ritron callboxes will need programming to match your frequencies that you use. You will need the software and cable, or your radio dealer can program them to your choice of frequencies for you.
With PMR446 radios, there are 16 publicly-shared channels, and if you want to find out if they will work well for you, get one and use the scan mode to listen to all the channels in your area for a few days. If you find some channels not being used in your area, assign them as your primary channel, plus find a backup channel in case there is interference from someone else. Everyone has the ‘right’ to use any public channel, and you cannot ask anyone to stop transmitting or go to another channel, even if you have an incident to report.
Also, it doesn’t need to be said, but do not transmit any private, medical or protected information on the radios. Anyone can listen in.
Hope this helps.