The young mother had been looking at her son's dick for a long time and he took advantage of it. When no one else was in the house he easily tricked her into sex. And as I see it, this hungry female didn't mind letting him see her charms. Only she didn't expect him to get that close to her ass so fast. But it was payback for her lust.
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.
Who lives in Bishkek?