They were raised as brothers .. but they aren't brothers, even in a legal sense I guess. If Yu's mom was able to call him back I doubt she ever gave up her parental rights and his birth certificate should have his biological father listed. Then A's mom and dad would've just been his guardians, and it is stated that he's a foster child, a totally different from a adopted child. Yu knows this from when he was a child. Legally speaking, there's nothing wrong since the both of them might not even be in the same household registration.
What surgery did he have? I know he had a c-section but what other surgery did he have?
The one to regulate his pheromones
Ohh. Any idea how that works? Like is he having hormone injections? Took out a tumor? Or is it organ removal?