Well, as a parent of a 16 yr old, it doesn't sound that unfamiliar. We're pretty big on doing chores and have a set rotation, that goes for everybody in the household. We wouldn't be past asking a house guest for a week to pitch in on our routine, but most likely it would be helping out with our son's chores that week. We would never ask a house guest to do something involving tidying away other people's things, though! And most importantly, we would never complain about it afterwards. And, as I mentioned, we have a 16 yr.old, not an 18. yr. old. Big difference.
Maybe they seem to exercise a lot of control on him because they have a lot of conflict with him around helping out at home, maybe he isn't as mature as your daughter. It sounds a little like they extended the way they treat him to the way they treated her. I can completely understand why you're upset, though, they took it too far imo.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett