Hi, Milly's Mum, she was thinking more in terms of them being only cats, rather than confined in a room away from other cats. Fred and Vic, true ex-ferals, hardly ever go out as they have a tendency to wander; even Sam, an ex-stray who's been with me for a long time, went walkies for 24hrs - I suspect she was looking for Polly, who has passed on - so I keep them in more than I usually would. It doesn't seem to bother them at all. They have the run of the house.
The only other option, which she is considering, is to leave them as feral, to TNR the kits when old enough and mum as soon as kits are weaned.