The first post in this thread tells you what it takes to feather sex as well as make red a black sex links. Do you know for sure that the father was pure for the recessive fast feathering gene and the mother had the dominant slow feathering gene? That's the only way you can trust feather sexing. Was the father not barred and the mother barred? That's the only way black sex link works. Was the father pure for the gold gene and did the mother have the silver gene? That's what it takes for red sex links. For all these the parents have to be set up correctly genetically. For black and red sex links the down color has to allow you to see the differences in the chicks. That doesn't always happen.
Tadkerson’s Sex Link Thread
http://www.backyardchickens.com/forum/viewtopic.php?id=261208
Are those true Ameraucana? That can get a bit complicated to answer. Does South Korea have their own Ameraucana standards, do you recognize the US standards, or are there none in SK so you want to use the US standards. Each country can have their own unique standards for any breed. So which standards are you using?
I only know the US standards so I'll go with those. Did you hatch those eggs? What colors were the shells? If they were not all blue but some were green, brown, or white colors they are not US Ameraucana. Did you see the flock that laid the eggs? Were the breeding chickens segregated by color so the roosters were only breeding hens of the same color/pattern? If different colors/patters were allowed to interbreed they are not US Ameraucana.
Looking at the chick's leg colors I don't think those are Ameraucana. Hopefully you will get some blue or green egg shell colors out of the pullets. Good luck!