Responses
Some could be actually because they are born from the same artificial womb but it works differently like they are related only to the ones with the same genes/sperm. Like Charin and Tehir come from the same fathers family tree something so they are genetically related and that's why Hyehan wants to abduct Tehir.
Spoiler
You could say some for characters tho that they could be brothers or more like the same person...you'll see in later chapters.
I have to say, if they were created by the same thing as this kindergarten project, then aren't they all brothers..? Sure is a lot of incest