All the crew and ground staff are definitely real.
Some of the passengers are BA staff and some are actors/models, none are real passengers.
In the recent TV add, the two cabin crew are both real crew, the girl is a E/F crew member and the man is a M/F crew member and some of the passengers are also BA staff pretending to be passengers.
Same in the Aviator advert too.
We often get invited to apply to be part of a campaign.