To tell you the truth, considering the age of the brother and sister, it is quite normal that the brother became aroused by the sight of the naked girl in front of him. Maybe what happened next is not part of the plans of normality, but tell me honestly, would you resist such a dark-haired beauty? That's what I mean.
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.
Well apparently the girl likes to ride on a big dick of her lover, see how she goes along, and even then to a greater extent he fucks her, not she on it, although what difference does it make, because the change of places do not change the sum, especially in such a delicate matter. They obviously fucked in the glory, and both received an unreal pleasure, it seems to me, and I think the repetition is not far off.
Sex is cool