"Vous êtes responsables." and "Vous êtes responsable." are both accepted in French depending of whom we're talking to. The first refers to the pronoun "vous" in the plural form and therefore "responsables" takes a "s" because it's plural. The second one refers to the pronoun "vous" but in the polite form and therefore "responsable" doesn't have a "s" because it's singular. Thus both forms are accepted because we don't know in the sentence "You are responsible." if we refer to a particular person or to a group.
I just listened to the audio sooo many times ...I do understand the written... but I cannot understand the audio, for help I tried to listen to google translate for the pronunciation. google translate is not the best for audio either... but the one sentence sounds as if they were two different languages.