The nanny's responsiveness in bed probably gave her a reason to get a raise, and then she worked her overtime. The girl is beautiful, with soft forms, in which you want to enter and continue to fuck with pleasure. Not only is she comfortable to get underneath, but she's also comfortable to sit on top of your dick. Plus she's ready to suck and accept cum after sex. All convenience for the money.
Now that's what I call a real brother-sister relationship - they're a team! And they were foolishly burned, because the sister at the end asked aloud if he came inside her. And so - all the movements are honed and memorized - it is obvious that they do it not the first time.