Ah weddings, my favourite part of Summer!
For Her:
Vann Morrison - Brown Eyed Girl (If that works of course
)
Bobby Darin - You Must Have Been A Beautiful Baby
For Him:
Five for Fighting - Hundred Years
Kenny Chesney - Young
Together:
Frank Sinatra - The Way You Look Tonight
Edwin McCain - I'll Be
Personally, I am a huge James Taylor fan so I would go with something like How Sweet It Is or Something In The Way She Moves.