okay now it definitely IS pseudo incest
Naah, she's basically using the dad as a beard, and the dad is using her as a convenient nanny (with perhaps slightly unusual motives) - it's all strictly business, and no one's confused about any of it.
. . . except Ruan Tao, who may have some understanding that her dad is using Su Man for his own ends (it's not like a trophy wife is an unusual concept), but there's no way she realises her new step mother has the hots for her.
How well this story handles their relationship going from where it is now to something more romantic is the big question . . .