just to clarify things if anyone is confused,
their father was infertile (couldn't reproduce children), and so to work around it, his brother (uncle chang-in) agreed to donate his sperm. since there were two of them, and that biologically, uncle chang-il was their father, he wanted to take one of them to raise as his own son. they were supposed to be treated as if both twins were cousins, keeping both of them in the dark. however, since they were close and attached with each other, uncle chang-in gave up on the idea and let the two of them grow up together. but now that theyve separated, uncle chang-in wants to legally take one of them as his actual son.
