I haven’t read the webtoon, so anyone that has read it, *please* don’t comment any spoilers! Now to the theory:

What if Taeyong and Seungcheon are twins and because SC’s family is so poor they had to give one child up for adoption? Then Hwang, who needed a successor, adopted him? 

 Points to back this up:

1. Hwang already established he had some connection to an orphanage when he took Munki on to work for him. It might be the same orphanage he potentially adopted Taeyong from? 

2. The boys have the same bday.

3. When Hwang sees TY the boys don’t switch butwhen SC’s dad sees him, they do. Meaning: TY’s dad originally adopted him (presumably). SC’s dad could either be his bio dad or bio dad to BOTH boys.

Any other thoughts? 

yeah me too, if real Seung Cheon's father was not looking in his direction i would think actually the parents were switched somehow but maybe both are his kids