Can they be bred naturally?
Dog houses work too. You mentioned you had silkies you can count on them going broody and your cochins. Not so much the ameraucanas, they hardly ever go broody. I would start researching incubating, because it will be difficult to only rely on broodies. They may want to hatch at undesirable times or not when you want them to. If you want everything to be "natural" then i guess don't hatch. Although you cold hatch and put them with a hen to care for them. There is not way to make it 100% "natural" though. It is controlled breeding regardless. If you were to let them all go in a woods, they would fend for there selves, as they would have no one to rely on. You would ameraucanas breeding cochins and cochins breeding ameraucanas. They don't care if they are the same breed. So there are some aspects of it that are going to be controlled.