Thanks all. It wasn't a difficult decision once no.3 took up a teaching job in Berlin and freed the room up. We worked on the principle that it wasn't good to be where they lived - next to an airfield that was flattened a few weeks ago and was now 15 miles inside Russian held territory. A no-brainer really.
For anyone thinking of doing the same, the easiest way to find someone is to get in contact with a Ukrainian, or one of their social groups. The wife spoke to someone at work who is Ukrainian and they asked around the local community. You get pot luck because it isn't a beauty contest - they could be 20 or 120. Our application was sorted by a local Ukrainian lawyer, so it took 3 days to find someone and get the visa application filled and submitted. Forget the idea that someone in govt will fill the beds offered via their registration scheme. For your part all you need to give is id plus tick a few boxes such as you have to get a landlord's gas safety certificate, which in my case cost nothing as the guy who does my safety certs, did it for free, but would otherwise cost about £50. You also need a smoke alarm on each floor. They will do a DBS check because there are obvious safeguarding issues around children, and most of the people taken in will be lone women or ones with children.
Language issues or not, it will work.