How we cite our quotes:
ENGSTRAND. What the devil do you mean? Do you set yourself up against your father, you hussy? (1.34)
Engstrand knows he's not Regina's father, and there seems to be some evidence that she knows it, too. The idea of family is one of the social conventions Engstrand manipulates to his own advantage. He does the same thing with religion.
MANDERS. But a daughter's duty, my good girl – Of course, we should first have to get your mistress's consent. (1.127)
Engstrand has set Manders on the case of getting Regina back to town. Manders is happy to oblige.
MRS. ALVING. Ah, but here he has his mother, you see. My own darling boy – he hasn't forgotten his old mother!
MANDERS. It would be grievous indeed, if absence and absorption in art and that sort of thing were to blunt his natural feelings. (1.154-155)
This assumption of filial loyalty is one of the "ghosts" Mrs. Alving clings to until the very end of the play.