@brainman
well, it should prove why she abandoned her daughters in the first place, and I don't think she'd come out with every bone in her body. Furthermore, I don't know how it works in Japan, but in Europe for cases of foster care of minors there is a tendency to give preference to the choice of the latter if they are considered mature enough. If Hotaka, Chii and Chika were to say in front of the social workers and the juvenile judge that they wanted to stay with their older brother, their mother would have little to do but take care of them financially (although she might be entitled to some days to attend them). But considering that having her daughters with her seems to have been more of a splash of the moment, to play "happy family" with her new husband, I doubt that woman would bother to get caught up in a trial that could take months if not years...
@Rasz
he bought her dinner, much more than a cupcake XD