Something had to be done though. So, after I put them to bed this evening, I moved the fencing around. I'm going to rest the Pampas grass and the grass around it for a couple of days. In the meantime, I've opened up the area previously reserved for Tilda, which has suitable shelter shrubbery in it. Tilda hasn't been out very much in the last few days - her choice, not mine - and I'm running out of options. Hopefully the grass in the usual area will perk up after a couple of days rest, and the Girls can go back on there.
Custard and Milly are continuing to behave well. They do not resist when I pick them up to put them in the other run for the evening, and often go in themselves with a bit of encouragement from me. They aren't particularly chasing Poppy and Lotti when they are all out together, so that's progress.
I can't risk letting them sleep in the main cube again at the moment. Poppy and Lotti are so noisy in the mornings (and get the others wound up so they start too) that we're having to shut the pop hole at night to try and stifle the noise a bit. If letting Milly and Custard into the main cube with the pop hole open is a bad idea, you can imagine why I can't risk letting them in if the pop hole is shut.
Not sure how we're going to resolve this one. If we were going into winter then the dark mornings would solve the noise problem.... but we're going the other way.