@deedeelicious: I don’t suggest wearing only a vest. That’s too casual for your dresses, and isn’t a very good look with classic menswear – it’s best left to streetwear/denim/casualwear. I agree that any kind of formal, or semi-formal, wear will look a little out of place in this context, but not atrociously so. My suggestion is a suit. Does your FI own any suits already? Either navy, or charcoal are better options than black, in my opinion. If your FI wants black, he should wear black, but I would see if you can convince him to try on some navy and charcoal suits – and you can get charcoal that is extremely dark, and he may like that – as they are both much mre versatile, more classic, more stylish, and generally better on anyone. That said, he should still pick his suit (as it sounds like he did). And, if he really wants to wear a Tuxedo, he should get that. No reason you can’t make suggestions, and explain your reasons for them, but be sure that you let him make the fnal decision, and that he knows you’ll be happy whatever he decides (withn reason).
http://www.blacktieguide.com is a must read; I wish it was a law that you had t read, and pass an exam, on it before wearing a Tux 😛
All of this aside, the Tuxedos will not look ridiculous, by any stretch. The tradition in North America is to wear Tuxedos to weddings, regardless of the classic, or traditional factors that would normally affect what one wears, including time of day. The dresses are full length, but of casual material, and more casual styles. So, you’re on the cusp of formal and informal (suits being informal). A dark, solid suit would be most appropriate, in my opinion. Vest or not is down to personal preference at that point.
I think a jacket and tie are de rigeur, here, as your dresses extend past the knee.
What time is your wedding?