Most important advice: Do not let this relatively small issue spoil your holiday in the USA.
Step 1: When OLCI opens see if there are any pairs available.
Step 2: If no pairs are available, do not select a seat and
cancel check in.
Step 3: Check again on the morning of your flight since some people might have cancelled or moved - if there are pairs then select them and proceed as normal, if not cancel check in.
Step 4: Proceed to airport and see if they can help you there.
Step 5: See if you can swap onboard.
Step 6: If nothing is possible, take your individual seats and look forward to your time together in the USA - not sitting together on a plane represents only a few hours of your life and I would not let it spoil the holiday.
Finally: to avoid future disappointment, pay now for ASR on the way back!
