I finally called on this since our trip is coming up soon.
I asked for UL J and was shot down by two different people. To add insult to injury, they are going to do a rebooking on UL economy and charge me the $125 per person "fees" that UL imposes. Holy terrible deal, the flights are around $250 on UL.com, so the idea of paying 10k avios PLUS $125 for that seat is a non-starter.
Frustrated to see in the CX forum that CX is at least protecting people in same cabin on either SQ or UL. I am totally underwhelmed by BA here, think I'm going to have to either try again and if no luck take a refund and just pay cash.