The concept was original and interesting, it leads to darker tones.
Developing it a series or a longer film would allow the main characters to develop or we could understand better their past and their thoughts.

SungWoo is an interesting character, with a devastating family history. If the new boy is the 11th, SungWoo probably repeated the brother reunion act many times. I understand his want to stay out from home.

The dad is interesting too. He obviously is selfish, leaving his son with the desolate pieces of his wife, but he kept looking for actors?, boys grown up in orphanage?, whoever wants a family?, to play the part of the brother that came back. Where did he go (or why) is not known.

SungKyu is the most difficult to understand, hence the ask for a longer version. If I get his crave for a family and a mom, it's interesting how he relates with SungWoo. I'd have done everything to make him like me, while SungKyu even threaten to out him to his parents. Apparently he's attracted by SungWoo too (they have an extraordinary sexual tension is such a short time), but the end left us wondering. He's a nobody, okay. But why that painting, emotionless face in the last scene?