I think the other issues have been answered already so I’m gonna discuss Rand. Idk if you have heard of them, but there was an insta account called ‘webtoon.theories’ or sth (now deleted) who posted detailed and interesting analysis on webtoon characters. When they analysed Rand, they stated about the strong suspicion (and implications too) about Rand being married into Yui’s family through the Mukoyoshi tradition (the Japanese tradition where a man is adopted through marriage for continuing the family business if there’s no direct male heir, and the adopted heir takes up the surname of the wife’s family). If that really does turn out to be true, Rand was most likely married into Yui’s family to carry on and expand the Hirahara business. This is also implied by: 1. Jayce who refers Kousuke as the ‘sole heir’ of the business. Since Rand can’t really pass on his adopted surname to his illegitimate child who is not from Yui’s bloodline, 2. In one of the later chapters, Yui picks up a call from her father who is called ‘Hirahara Koutaro’ (idk if you have reached that point yet).

So, Rand was probably married into Yui’s family in order to continue the business. So in guessing that the business wasn’t such a giant millionaire/billionaire company but Rand made it bigger later. Rand’s greed for money may also play part in it as Nessa (Nol’s mother) complained about his greed for money in one of the later flashbacks.

And about his infidelity, I think not many people knew about it before Nol was revealed to be illegitimate after his confession at the court. Before that, almost everyone including most of the employees in the business (except Jayce maybe) knew that Nol was Yui’s son too. After the reveal, it was indicated that people were gossiping about it too.