@Jockpo523 You mean what if Shirogane's mother is actually Shinomya's stepmother? Maybe she married into their family after she left with Kei (she wanted a more successful man and a more comfortable life after all), and here, Shinomya encouraged her to run away, what she doesn't remember for some reason... So here we have the problem that Shinomya and Shirogane are actually siblings, not related by blood at all, but that's why no one from Shinomya's family will agree and wants them to break up. It really sounds crazy but it might be...
another university... this cliche, I agree it will be the case, whatever the reason will be (marriage or just parents not approving them dating), even though it makes me very disappointed... I would say her family can make the university not to accept HIM more like her... (destroying someone else chance feel worse than your own, so it's more likely she won't oppose)
About the engagement, this part came to my mind too, but I really hope it won't be the case, as it add a seriously annoying amount of drama and shit...