Probably all of them are mixes, not pure breeds.I found it in my yard actually. The black one that is and the older one was given to me. The last 2 I just got from someone who raises chickens but I think they aren't 100% sure what breeds hatched haha...they told me one is a Ameraucana and the other is a cream leghorn but I'm not sure they are correct. The brown one with the stripes came out of a brown speckled egg.
Or they may not really be mixes of specific breeds, but might be chickens who never did have purebred ancestors. I don't have a handy term for that.
There are no Ameraucanas in your photos. Ameraucanas have pea combs, blue or black legs, and muff/beard on their faces.
Three of your chicks have single combs.
The other chick has green legs.
I don't see muff/beard on any of them.
Some hatcheries sell "Americana" chicks (changed spelling to confuse people), that are not purebred Ameraucanas but are supposed to lay blue or green eggs and look sort-of like Ameraucanas. They are actually mixes of one sort or another. There is a chance that green-legged chick with the reddest comb might be one of those.
I haven't heard of a Cream Leghorn, but Cream Legbars are pretty common (the difference is in the -bar instead of -horn at the end of the name.) Ameraucanas and Cream Legbars are breeds that lay blue eggs. Any chick that came from a brown egg is something else, not either of those two breeds.