Did Phillipos father his daughters children?

Possibly, we don't know. They are either his or one of the men he has sold her to. They mostly call him Grandfather, except Myrto who he says is his youngest daughter.

I think they might be, mostly because he is such a control freak. We see him giving her a pill on a number of occasions. Before knowing the relationship of the children I assumed he was giving her the pill. I still think it might be, and that he does this to ensure that she doesn't get pregnant to anyone but him. We don't see him give it to her after he is informed she is pregnant. Also he seems fine with her being pregnant, someone who is as violent and as controlling as he is, would surely have reacted very badly if her being pregnant was not something he liked happening.