I have had this (almost) exact scenario, albeit on my return journey. Incoming A380 went tech en-route to SFO, re-routed on VS in J.

I claimed 75% of the segment value as reimbursement under EC261. BA denied it for the usual spurious reasons, including that VS Upper Class = BA F, and I had to go to MCOL to get the money. In the end BA made a partial payment to my credit card and folded on the balance right at the end of the mediation process when I made it perfectly clear I’d be prepared to go to court. I imagine your monetary amount will be similar - mine was around £1k in total for both passengers.

If you’d like any specific pointers, please feel free to drop me a PM.