If you and your SO are on the same itin, I don't think one will be upgraded without the other. If you are on a separate itin, then option #1 can cause problems. If your upgrade has already been processed, then there's a good chance that the seat next to your SO has already been assigned to someone else. If you turn down the upgrade, you'll be put somewhere else in coach, not next to your SO.
As a Plat with a Silver wife, here's what we do when we travel together.
1. I book us on the same itin, give her an aisle and put myself next to her.
2. I separate the itin so our upgrades will run at our respective elite status EUA window
3. If I upgrade before the flight and she doesn't, I put her on the companion list at the airport.
4. If she doesn't get a companion upgrade, then we flip a coin to see who gets 1st (strangly, she wins the coin toss a lot
) and the other sits in an aisle seat