I've left this comment on multiple series over the years, and I hate that I keep finding more places to do so; "It was all a test" is never a good trope.
So, you can't welcome her because she was traumatized by your little sister after she disgraced both of them and lost them nationals in front of everyone? I understand that there's some nepotism involved, but holy crap are your values screwed.
My guy, you know how mischievous this trio is and you work in manga publishing, where all these tropes and cliches thrive; why would you accept the invite to bathe first when you should know full well what they're plotting? If he acts surprised to see them next chapter, he's faking.
So far, I think the business team wins. These are supposed to be hidden talents, but cooking class cooked and the cheerleader team looks like they're going to do more cheerleading. The business class actually being capable musicians is definitely a hidden talent.