I'm planning to wed two pairs of very close neighbors sometime soon. My plan is to gather the main characters in a temporary household to keep them controllable: Pair A, one spouse's parents, Pair B,...
I never tried, so it would be interesting reading how it will work.
But, I would expect the game to run one wedding at the time, because the arch does trigger music and confetti etc, and I don't think it was designed to overlap.