I think you got it wrong. The teenage girl that thinks she's being sold off to the Beom family is actually a flashback memory of the mother when she was young. Her family was trying to marry her off to Teaha's father!
As for Hae-soo, the older brother (Taehee) is actually trying to lure her into his grasp by sending one of his men to the hotel job she works, and propositioning her boss for any extra employees she may have available to work this "emergency position" they need filled. Taehee is going to have her work at that lounge he routinely frequents for drinks and prostitutes!
Keep in mind, during all of this, Hae-soo has never told Taeha that she was looking for extra work to gain more income to get a new apartment. He has no idea what is about to happen to her if she takes this fake "new job". This is a perfect underhanded plan for taehee to subtly snatch Taeha's woman from him.
I'm not going to lie, I got confused at first with that teenage girl, but I saw that she had a striking resemblance to the boys' mother. That's when I realized the author started telling her side of the story and how she got involved with the Beom family. The author is weaving her juvenile backstory into the current storyline every now and then, however, they're not doing it in a way that readers can pick up on easily. I still have to reread certain sections of each chapter where it's done two or three times to catch the transition.
Not it's not flashback of the young mom it's a new girl for tae ha ( it was supposed to be tae hee) she may ressemble to the young Mother because that storyline may be a parralel to young taejoo and young miss baek ( the step mom). As for the chapter i can see where it going, we About to enters to a story swicth with beom drama, na hae soo gonna be a escort and may assists one of the men in the exposition events , it's how she will find About the new job and will spiral , so she will not Contact tae ha back beacause of it, it feel like we about to enter a tsunami of drama , that drama may be the arc to made her character stronger and darker, she needs this before she enters into that beom family as the future beom lady. As for mincheol 's arc there are had been some hint that he may plan to scam ari with a wedding fund, i believe the focus will get to him when na hae soo will become a beom and indifferent to him ,while he will success to pay debts beleiving he was saving her , but she find out she got a rich man and don't give a huge Fuck about him + a new personality, this will be a slap to his face
Not it's not flashback of the young mom it's a new girl for tae ha ( it was supposed to be tae hee) she may ressemble to the young Mother because that storyline may be a parralel to young taejoo and young miss baek ( the step mom). As for the chapter i can see where it going, we About to enters to a story dark swicth in the storyline with beom drama, na hae soo gonna be a escort and may assists one of the men in the exposition events , it's how she will find About the new job and will spiral , so she will not Contact tae ha back beacause of it, it feel like we about to enter a tsunami of drama , that drama may be the arc to made her character stronger and darker, she needs this before she enters into that beom family as the future beom lady. As for mincheol 's arc there are had been some hint that he may plan to scam ari with a wedding fund, i believe the focus will get to him when na hae soo will become a beom and indifferent to him ,while he will success to pay debts beleiving he was saving her , but she find out she got a rich man and don't give a huge Fuck about him + a new personality, this will be a slap to his face
Also, I can see what you're saying with regards to the father offering up one of his sons for a business marriage.... But the man sitting across from her at the table does not have a mole under his eye like Taeha does. Also, the father has a slightly different facial structure than Taeha (it's subtle, but it's there). Then there is a dead, ice cold glare in his expression. Even when Teja is serious or pissed, he still has more expressiveness in his eyes and never looked that deathly sinister. (⊙…⊙ ) That dude feels too much like a younger chairman, but I do see your point, as the chairman thinks both of his sons are "free"and single, and he is in the process of trying to see which one of his sons can be his successor for the family business.

I AM SO LOST