Yes group number currently only reflect the individual's status and cabin with no reference to others on the same PNR. This will change at some point in the next few months. They will be able to board with you though, and the advice given by BA on travel support site states:
https://www.speedbirdclub.com/mediaL...-27Nov2017.pdf
Please note that priority boarding will not be reflected for any other people travelling with an Executive Club Member on the same booking at the moment, but will be introduced in the coming months. In the meantime, the whole party can use the priority boarding lane and our staff will endeavour to board everyone together.
B34 at Geneva this evening (GVA-LGW) travelling with my parents (both blue), all on the single HBO booking. As expected groups on BPs showed up as 2 for me and 5 for my parents. Boarding was called as 1, then 2 and 3, then 4 and 5, with right hand lane for 1, and then also 2 and 3, and the left hand lane for 4 and 5. We arrived as 4 and 5 were called, but went to join the right hand lane for 1, 2 and 3, but on reaching the front my parents were kicked back to join the 4 and 5 queue and were not allowed to come through with me, and so we all ended up traipsing back to join the 4 and 5 queue.