Well, since I wrote that post yesterday, I've been watching them closely and it doesn't seem so bad
...I really don't know what to do so I've decided to keep a close watch on them this week and decide then. It will mean buying a new cage as I'm going to be using the spare Rex we have for our new arrival but that's no problem - I have a small emergency cage in case of bloodshed but it's not big enough for a hamster to live full-time in.