Despite the wiktionary entry, I have rarely heard "you guys" in Australia, except as a joke. And Australians, being native speakers of English, are unlikely to learn their English from an American television show: most learn it at their mother's knee.

But to answer the OP's question: yes, I do think the use of "you guys" by the receptionist was odd, and perhaps over-familiar, but I suppose I'd take it in the spirit it was intended (although it might not have been entirely obvious what that spirit was). If the receptionist was using the expression simply because you were Americans, then that seems a bit puerile.

As to the passport thing, I have seen that form of words on a check-in form in a hotel in rural Scotland. I assume that it might have been a requirement many years ago. The term "British subject" is very out-dated in most contexts now. The primary status of the people of the UK has been that of citizen since 1949, although they remained British subjects as well as citizens up to the end of 1982. Up until then, Commonwealth citizens were also construed as British subjects under British law (but not under the law of all Commonwealth countries). Since then, British subjects form a residual group of people who were formerly known as "British subjects without citizenship", and consists primarily of a few people connected with the UK via Ireland or India. So the wording on the form is an absurdity, as the OP rightly hinted.