5Bets
Mrs. Oikawa and Mrs. Iwaizumi knew about their son's relationship. They may be able to hide it from everyone else, but a mother knows their children. It was pretty obvious once you think about it. Tooru and Hajime have been inseparable since childhood: always by each others' side, staying at each others' house, cuddling on the couch, what they thought is discreetly holding hands, etc. Tooru even managed to pull Hajime into volleyball, which they both ended up being obsessed with.
Even on the court, they were inseparable. They were the unstoppable duo once they got better. They grew up together, played together, and ran the team together. Hajime also kept Tooru in check which Mrs. Oikawa appreciated.
When Tooru injured his knee from pushing himself too hard, Hajime took it the hardest, besides Tooru of course. So when Iwaizumi seemed to be more overprotective of Tooru, it didn't surprise their mothers much.
So, yeah, they weren't surprised by their relationship one bit. They probably even noticed their feeling for each other before their sons did.
While their sons are blissfully oblivious to their mothers being knowledgeable about their relationship, the women think that they'll tell them when they're ready. Although, that doesn't mean they won't innocently ask questions to make their sons embarrassed.
Mrs. Oikawa and Mrs. Iwaizumi ended up making bets on the two like who would realize their feelings and who would confess first. The latest one, however, was who topped who.
While that does seem like an invasion of privacy, it's not like they're actively trying to find out. They honestly don't think the two have done 'it' yet anyway, not that it's really any of their business. This doesn't mean they won't argue over who it would be when they aren't in their son's presence.
One day, when Tooru was over at Hajime's, Mrs. Oikawa received a call. She answered it to Mrs. Iwaizumi singing "Your son is a bottooooommm!" to the tune of Girl on Fire by Alicia Keys. The first thought that came to Mrs. Oikawa's mind was that she now had to fork over 5000 yen, but she secretly was glad that her son was happy with Hajime.
When Tooru entered the house the following day with a slight limp, Mrs. Oikawa couldn't help but tease with, "Tooru I know that's not you knee acting up." The following blush that followed made the loss of 5000 yen to Mrs. Iwaizumi just a little more bearable.
And if the boys were present when Mrs. Oikawa gave the money to Mrs. Iwaizumi while she complained about how her jokingly complained about her son not putting in enough effort to top, let's just say the two boys were a little mortified.
Mrs. Iwazumi followed saying that they couldn't hide anything from them. This resulted in them both being embarrassed mess with Tooru hiding his face in Hajime's neck. But their sons were happy together, so they supported them all the way.
And if they bet on which one of their friends would find out about their relationship first (Matsukawa and Hanamaki), it wouldn't change anything. And if they then followed to bet on who would propose, it wouldn't change anything either. And if they decided to embarrass their sons by mentioning these escapades at their wedding, it wouldn't matter because their sons were happy so they were happy.