Well, the problem is that the alternatives here offered aren't "correct English"; they aren't INCORRECT, but they use a type of English construction that does not reflect how most people write, much less speak, Modern English. These "rules" about not separating prepositions from nouns and pronouns, among other similar  curiosities, have their origins in a style of elitist prescriptivism that mostly originated in the 18th century, I believe, when it was fashionable to model usage off of Classical Latin. They didn't (probably) at any time have much to do with how the vast majority of people actually used the language (what modern Linguists would call "correct" usage), but seemingly had more to do with creating a culture of exclusion to signal status. But in any event, even if they were more widely used in the past they certainly are not today. "Whom", on the other hand, is an entirely separate and interesting case, with a long history of correct usage--but most would agree it's now almost completely obsolete in any sort of standard English.

In short, no modern person would say or write "With whom are you going on holiday?" unless they were making a deliberate statement, or had some other very specific purpose in mind (like for instance, writing Jane Austin fan literature). "Who are you going on holiday with?" (or in the US, "Who are you going on vacation with?") is indeed the normal, correct form in standard dialects of modern English. I would add that if the "with whom" form helps Spanish students as a model for wrapping their heads around the proper Spanish word order, that's great--but to suggest it's the more "correct" form is inaccurate.