Well, at the moment where Wahei said, "its up to you to decided, think about it", I know where this is going.
She will decide to go to her mother. So cliche. LoL.
Wahei should man up and really put himself as a Brother to this sisters. This is not story about a Man with Stranger Kid, but they literally are half siblings. After all this long, the story focus on family. If Wahei really their family, at least give some advice and though about this situation, especially the mother that literally neglect her daughters. Cmon, Wahei is an adult, so he have a though about this kind of people, or at least he can help with asking people around him (office friend) about this matter.
Now, he just literally give a decision to a confused school girl. Without any adviced or though as an adult. If this turn to be smooth sailing between this mother and daughters, its good. But what if they got abandoned again? 2nd strike for them to get hurt "again"