The characters are all affectation - Angarano's not a bad actor, but he's been instructed here to be constantly "on," and maintains a nonstop level of energized patter that's meant to be amusing, and never is.
It's one of the least-effective charm offenses in recent movie history - thus, we are thoroughly unconvinced when it seems to penetrate the defenses of the bride.
She herself is a wounded soul whose problems are traced to family tragedy (The Cliche in the Rye), leaving an unhealed wound that is her brother (Jake Johnson), a belligerent, suicidal drunk (also intended to be colorful/touching, also not).
A running joke has Angarano's neurotic buddy (Reece Thompson) trying to flee the wedding, and he's the one character who draws our sympathy because we so desperately want to leave this place ourselves.
And even he turns loathsome when he makes it known that he intends to sleep with "the maid." He doesn't bother to learn her name, and gives up when she doesn't speak English.
Who laughs at this?
I won't go so far as to say "Ceremony" is racist, but it does make aren't-they-cute use of African characters in tribal gear, on hand for the amusement of the ascot-wearing, cocktail-slurping coterie of documentary filmmakers and children's book writers/illustrators.
This wedding doesn't need to be crashed. It needs to be attacked by an Apache helicopter.