Well, half-brothers and half-sisters are not related at all, so it can't be considered something bad or immoral. It's no surprise that an adult guy and girl, with no regular sexual partners and almost daily being around each other, suddenly felt attracted on a sexual level to each other. Considering that the girl liked it (the guy then no question), I think they will continue to practice this kind of thing from time to time.
It's a curious topic, especially against the backdrop of molestation scandals at work. They yell a lot, but the video, where the brunette supervisor gets into the underpants of a subordinate, immediately receives a mountain of likes and approving comments. Which is absolutely correct: nature takes its course, and it does not matter where, at home or at work, two adults have sex at their mutual desire.
♪ I'll be there, too ♪