Ooh, I love big Italian weddings! Definitely glam it up babe Daytime, go for a shorter ****tail dress, if it's an evening do, go full-length (or at least mid-calf).
I love Grace & Hart dresses for more formal stuff with a cute party edge, google them and check out their stuff, they do a lot of cute, short dresses but also a few longer and full-length things, at the very least it might give you some ideas if you decide the dress you have isn't going to cut it Chiffon does go pretty well for formal events though so sounds like you might be on a winner! I'm a big fan of taking a, well, not really 'plain', but ykwim, dress and going OTT with hair, accessories and shoes, kwim?

Good luck hun, I hope you have a great time at both dos, and my congratulations to the happy couples!