4) The "Vitelli" in Latin would be the vocative of the name "Vitellius" rather than "Vitellio".
Cool sentence -- I had never heard of it before!
The Latin etymological equivalent of the Italian sentence would be "illi vitelli de illis Romanis sunt belli", which uses "de" in a way that's unidiomatic for ancient Latin (where it only means something like "from", not "of" in the sense of "belonging to").
1) Is correct Latin
2) Sounds Italian, not Latin
3) In Italian it would mean "God's veals are beautiful"
4) In Latin it actually means "Go, Vitellio, to the sound of war (made by) the roman God"
[0]: https://it.wikipedia.org/wiki/I_vitelli_dei_romani_sono_bell... (didn't find an English version of it)