In My notion only "im Urlaub" is often in use. One other two variants may be legit. But I do not know anyone indicating "in Urlaub" and I might say "auf Urlaub" is just slang. Follow combined with the online video beneath to see how to put in our web https://bihlmayermedia-bilder.com/urlaub/wir-sind-im-urlaub/