A daughter must obey her father or punishment will follow immediately. Otherwise there will be no discipline and order in the house. And the fact that he checks her pussy is just parental control. Her father has a right to know who she hangs out with, where she goes. By fucking her, he showed her who's boss. Well, you can't pound the table with your fist like a barbarian. Giving her a blowjob and cum on her tits is the best way to raise her and show her fatherly concern!
That the sister is interested in her foster brother's opinion is commendable. And assessing her worthiness from a man's point of view he can. But asking him to jerk off in front of her is kind of weird. He's going to get her, isn't he? Only this slutty girl is not scared at all - that's exactly what she wants. He ended up flushing a whole puddle on her tummy! Drove it.
...and then lick it all off her beautiful breasts...