a bit of Italiano

Italian girl, here
First thing, the last name "Vitale" is actually most common in the South of Italy, not the North. So either you could find another one, or change their provenance from north to south.

For the words: father would be "padre" but it is quite formal. You could use "papà", which is the equivalent of "dad". Note that it has the accented a which you may not have on your keyboard. (The word "papa" without the accent means "Pope" -not to be confused! )
For mother (which would be "madre") you can use "mamma" (Mom).

If they are religious, they wouldn't actually use religious exclamations, I think? If you still want to use them, "Dio mio" is used usually to show shock (ever seen those old ladies, hands in the air, rolling their eyes heavenward?). "Santa Maria" -not really used (maybe more in the past).. depends what you want those exclamations to show.

For the guy courting her - caro (dear), caro mio (my dear -used also as "You'd better bring me a prettier present next time, caro mio"), amore mio (my love).

I hope it helps, I'm happy to answer more questions

"Che bello regazzo" is what I hear in Italy re: OMG, what a handsome guy!

My pleasure
On the South/North: most Italians who emigrated where from the South anyway, so if it should come up, I would find it even more believable.

"Che bello ragazzo" is "technically" correct but we don't say it. Instead we say "Che bel ragazzo".
For the "OMG, what a handsome guy!" it depends. Considering you are talking about almost a century ago, she would probably say something like "Oh cielo, che bel ragazzo!" (Without saying it to his face I should think ). Or "Oh Dio, che bel ragazzo!" (or the even more colloquial "Oddio, che bel ragazzo"). If she says it aloud, her parents might tell her to not name God's name in vain, depending on the family.

For the nickname, "caro" is more a term of endearment, but it's not common to say "Caro George" as in "Dear George". When you say caro, you often don't need the name, basically, unless she is talking about him to someone else (as in "my dear George brought me the loveliest flowers yesterday").
For parents: " Ma' " and " pa' " are common abbreviations for Mom and Dad (yes, the same as in English!), although in 1913 the family might be a bit more formal. I can suggest that you just use the English version (so capitalized and without apostrophe: Ma & Pa), but that's entirely up to you, of course.
And, it comes to me now, they could use "babbo" which is sort of "daddy" (Santa Claus in Italian is "Babbo Natale" -figure that!), and is between father and dad, and would be more used then that in today's Italy, but still well known. A diminutive would be "babbino" (ever heard of the aria "Oh mio babbino caro"?)-there is "mammina" too (Mommy).

Hope it helps!

Moriar said:

My pleasure
On the South/North: most Italians who emigrated where from the South anyway, so if it should come up, I would find it even more believable.

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+1
Not too long ago I read a book about the Triangle Shirtwaist Factory fire in New York City. The employees were mostly immigrants, mostly from Russia and Italy. The Italian immigrants were mostly from South Italy and immigrated because drought conditions made farming difficult, plus (IIRC) most of the land was owned by wealthy Italians who lived in the north and leased it similar to tenant/sharecropping.