"Do you have the passports?"
Translation:Ovatko passit sinulla?
You have to use "ovatko" because passit is plural. The word order also works better in the original sentence because it emphasizes the word passit so it matches better with the English "THE passports". In spoken language I think your sentence works and "Onks sulla passit?" is something I would say, but in written language without additional context it doesn't work that well.
Yeah in spoken language that is so common that I now started to completely question my own Finnish skills too (and I'm a native)... If it was indefinite aka "Do you have passports?", then it would definitely be "Onko sinulla passeja?" (plural partitive), and now I'm seriously wondering if you do use 'ovatko' or 'onko' with definite article, because usually the ownership uses 'olla' only in the 3rd singular form.
But I think 'ovat' is correct because if we make that into a statement, it becomes "Passit ovat minulla." But it sounds unnatural to say "Minulla ovat passit." and I'd actually rather say "Minulla on passit." but here I am already losing the vague line between spoken and written Finnish... maybe I need to educate myself a little bit more about my mother tongue :D