you can always refuse an upgrade once it's cleared. i would definitely prefer to take my chances until the door is literally about to close, as you both are elites and thus are eligible

i have flown with non-elite companions and noted that my charms never worked on the gate agent to upgrade them. but, the person sitting in my pre-assigned seat (next to said companions) is generally happy to trade places with me
unless, of course, the companion does not desire the seat up front himself...

what flight is it? i can take a look at expert flyer for ya to see how it is looking

p.s. refusing the upgrade at the gate can create a mess with your seat assignments.. so i prefer to have that power myself. plus... the greatful looks, smiles, and thanks, can make your flight