Question...can you help?

I had not one but THREE young hens, (not even 6 months old) go broody in the dead of winter....lots of snow and frigid cold temps. . So I ended up putting some fertilized eggs that I got from a guy I know under one of them. 4 hatched out, so I left her 2 babies and stuck one under each of the other mama wannabes'. They are each in a nesting box, there are only 4 total boxes and 3 are being used up by the new mamas and their babies. My question is, I am going to have to move them somehow, and I need to know what would be the best option for this? Do I need to quickly buy something to house these 3 hens and babies? The house they are in now, the boxes are up off the ground at a height that if/when the babies decide to fall out or fly the coop they couldn't get back in. The other hens that occupy the hen house will most likely kill them. Yesterday one of the mamas let one of them in her box to lay an egg while she was sitting on her chicks! The hen house has a heat lamp on 24/7 in the cold temps so whatever we end up doing we will have to get another heat lamp for them too...
thanks for any and all advice.