Just been going through the groups blurb and I could only find info about the pre-seating, not about baggage as follows:

"It is essential to divide eligible customers for pre-seating from the main group booking
i.e. Executive cardholders, families with infants etc before the main booking is queued to
British Airways for a seat map request. Once a group seat map request has been
received, eligible pre-seating will not be available for those customers and they must be
pre-seated along with the rest of the group"

This seems to show that as a group, it will not automatically allocate any of the benefits. I would think that the tickets will all be issued with the standard baggage allowance and then if an eligible pax has more than that at check-in, that is when the agent would check their EC tier.