The first experiment failed, so the uke only has human traits. The second experiment was successful, so the seme is half-orca, half-human, I guess. The uke is older because he was Experimental Subject 1.
I think it's only Haeil who is a product of kyungjun + prof Gu genes (might be also without prof Gu consent)
While hyoseo is prof gu and his wife's biological son (we saw the photo of his wife briefly in one of the chapters)
Maybe the uke didn’t get any orca genes at all and only turned out to be a clone of his dad. So, this might not even be incest.
The kids were created using the genes of one female orca and two human men, so they might be related through the orca side but not through the human side. Only one of the kids had orca traits, while the other one was completely human, I guess.