No, you only need to have a valid passport.
The language spoken in Brazil is Portuguese. Most of the services you will need there (airport, private driver, hotel, wedding, etc.) will have staff that speaks English. But it would be awesome if you could learn a few words in Portuguese.
If your invitation says “and Guest,” then yes!
Formal attire, please!
Yes!! We want them to be part of our special moment! There is a big kids space at the reception and workers that will entertain them while you party.