While this is true, I really don't think it justifies their treatment of him. Of course, we only have one perspective on it, but flameboy strikes me as a decent chap who doesn't mind doing his part in the household; the way he describes it, it sounds like they're treating him pretty unfairly.
Not that it matters, though; it's their house, and so they're the ones calling the shots. You could try taking it up with them, but judging from the brother situation, it appears to be the way things work in that house.