It's a dual-corruption scenario, and the story has only JUST begun. Of course he's wishy-washy about sexual encounters with his family to start off. It's a taboo. As the story progresses, he'll slowly throw off the yokes of social propriety, and, to go with your wishes,
bigphil963, I have no doubt that he WILL be able to tell the mother off. I suspect it'll be a choice between two paths. Son becomes the dominant one, or mother does. Big sis route will probably be exclusively her in the dominant position (unless there's also a blackmail submission route), other siblings will be mostly submissive, and wild girl will have something like a "true love" route and a domination route.