Good news, the principle is sound.
I did three tests and during two of those there was a slight delay between the two couples. During the second test they were in sync. First and third test it looked like this:
https://abload.de/img/16.12.19_20-47-349fk9g.jpg
All four sims started standing as close to the wedding arcs as possible before I gave the command and the game was paused.
Music: Only the track for the first couple was played. When the music stopped for the first couple, it also stopped for the second.
Household members (no free will): No auto-watch action was queued.
Summoned club guests: Didn't watch the ceremony. I hadn't placed chairs for the test though, maybe they'd sit and watch if I did.