I just read your answer to someone about sleeping arrangements on vacation. You wrote, "If it solves a problem of space or expense, a father can sleep with his teenage daughter in the same bed, and a mother with her teenage son." I would have thought that the mother with the daughter and the father with the son would have been the expected answer. Or was this a general statement about parents being permitted to sleep with their teenagers, of either sex?

Yes, this a general statement about parents being permitted occasionally to sleep in the same bed with their teenagers even (!) of the opposite gender, like on vacation. Pesach Kasher v'Same'ach! Rav Ari Shvat