BA would not be able to make any swap of seats. AA will have to release a seat as an award seat before BA can book or change to it.

Your best option is to book two separate but acceptable flights for the two passengers now, and monitor award availability to see if additional award seats open up. EF has an alert system that can help you monitor AA award seats. Once an additional seat opens up, you can call BA to change to a single flight (changes fee may apply).

Worst case scenario, you can go to the airport and ask to be put on the standby list. As a first class passenger, you do not have to pay any fee to standby. However, this comes with the risk that your standby may not clear. Also, if you prefer to travel together, consider asking the agent to put you on standby for coach as well.