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.
What was this mama thinking when she walked around the house without her panties on? So the dog smelled what the bitch wanted. When he pulled up her skirt, she had nothing to say. And she got all high and mighty when he sprayed his sperm all over her face!