Originally Posted by psychopompos

Numbers can be found here: https://www.britishairways.com/trave...xecutive-club/. If you have status and you're logged in you'll see the number which corresponds to your status.
One of you can designate the other one as an authorized third-party. That way both bookings can be done by the same person in one call. https://www.britishairways.com/trave...dpartynominee/
The Japanese call center should be opening precisely at the time when availability is released, but hopefully someone with experience of actually doing that will chime in.