Originally Posted by
Newbtravelle
Would this be a different situation if this was one PNR?
It wouldn't make a difference if one PNR and some had dropped out from travelling. Particularly at LHR T5, since 34 minutes before departure the computer would know that the people concerned were not in the building and would be merrily assigning seats based on BA's priorities, rather than the priorities of those remaining on the PNR.
Either way, you best cancel and potentially get some of the taxes back.