Here is a thought for you, if you didnt have room to move the hen, could you have blocked the nest off so that just 1 hen was in the nest and no others would have been able to lay in the nest while that one was sitting? That is what I do, when a hen goes to sitting, I block the nest hole so that others can not get in with her and then ever evening, open her nest hole up and allow her to get off the nest, eat, drink and poo and then when she goes back on the nest, I put the cover back over the hole.
All 3 hens could and may want to leave the nest after a few hatch, so what I would do is let a few hatch then take 1 hen off the nest with them few and keep the others on the nest til more hatch or the rest and then let those hens have those chicks.
I have been thur this before and what I told you will work. When this happened with me, one hen ended up being mom to all of the chicks she ran the other hens away.
I hope all works out for ya. Good luck with them and let us know how it all turns out..............