Ok so I think I FINALLY get the family relations and everything

"Hani" is not related to the company CEO and his real name and origin is actually unknown. 18 years ago the CEO started falsely claiming he had an omega son named Han Sangyul in order to promote his hormonal pharmaceuticals company and gain more investments/earn more money. But they never showed this son's face to the public, because he didn't actually exist. The company took in a bunch of kids hoping they could make them into omegas with the experiments they did on them, and pretend one of them was Han Sangyul. The only kid who survived the experiments was Hani, so they gave him the name and kept trying to make him an omega. But even though he survived the experiments, the tests still said he didn't become an omega.

Since they've been unable to produce an omega the company stands to lose a LOT of money and investments, so they instead made a plan to make sure no one ever finds out there is no omega son and get money from the royal family instead. The plan was to run a secret smear campaign against the prince who is an alpha, painting him as promiscuous and problematic in the media, and then pressure him into getting engaged to Han Sangyul, the only omega in the country and therefore the only compatible person for him (who never actually existed). Then they plan to break off the engagement after a few months, before anyone finds out he's not an omega, but claim it was the prince's fault so they can ask for monetary compensation for the prince damaging Han Sangyul's reputation and making him unmarriable to any one else.

The CEO decides to make his bastard son named Kim Chulsoo, whom he had with another woman, change his identity to that of Han Sangyul's, and be the one to enter the palace to carry out the plan as the promised bride. This is bc he loves him and wants to introduce him to the public as a legitimate son of his, which he obviously needs to have the same surname as him to do (Han).
This meant our Hani needed a new name, so he was given Kim Chulsoo's name instead. They decided he should accompany the real Kim Chulsoo/new fake Han Sangyul to the palace under the pretence of a study buddy, bc exposing him to an alpha might influence how the drugs in his system react.

I can't believe it's taken me this long to understand lol. Hope this helps anyone still struggling with it (づ￣ ³￣)づ