that should be fine - First Wing feeds directly into the Galleries First lounge, so the same guesting rules apply i.e. one guest each for passengers travelling in First and Gold BAEC members, or two guests for Gold Guest List BAEC members - guests must be travelling on a BA/OneWorld ticket, but it need not be the same flight
the only difference between these rules and what went before is that it was previously just about OK (normally) to squeeze an extra guests or two in at First check-in and then through fast track security - the guesting limit is now very strictly enforced in the First Wing since this leads directly to the lounges