In My perception only "im Urlaub" is commonly in use. One other two variants may very well be legit. But I don't know anybody expressing "in Urlaub" and I'd say "auf Urlaub" is simply slang. "In Urlaub" as in currently remaining there, looks completely Completely wrong in Upper-Austrian, but I https://bihlmayermedia-bilder.com/urlaub/wir-sind-im-urlaub/