Grats on stepping up and getting hitched. ^

Because it's within 72 hours of the flight, seat assignment may indeed already be under airport control which is probably why the MP hotline couldn't fix it for you the day before the flight.

I would try calling them 1 more time. Perhaps something has changed or a different agent has a better handle on the situation. I am surprised they split you. I assume you were on the same booking from the start ? Splitting you if you were on the same PNR is very strange indeed.