Just thought I'd update...
All 3 hens are mothering the 3 chicks and woe betide anyone that tries to come near! I'm amazed at how ferocious they are when protecting those little ones. They all took it in turns to try to hatch out some more but it wasn't to be so they scattered the eggs about and I took them off for composting. Initially mothers and babies were all in the hen coop, protected from predators but the chicks kept squeezing out and the mothers couldn't get them so we took a deep breath and let them all out. They are all quite happily free-ranging now and it's lovely to watch the mothers teaching them about foodstuffs, and scratching and dust baths - a constant chattering from them all

So for all my fretting it's all worked out very well following Nature's way. Thanks for everyone's help and hand-holding.