But BA is the issuer and they have a really bad policy on no refunds on short cancellations, I think you have to cancel > 24 hours in advance or there's no refunds at all on the Avios, although you might be able to get the taxes back.

If one person is a no-show I think it will be ok for rest of you but you probably won't get your miles back from BA. You can try to get your taxes refunded for that one unused ticket, which if is probably negligible.

-David