While the OP was asking specifically about priority boarding for a group (some of which were Concierge Class, some of which were not), I wanted to address several of the comments that say there is no priority/early boarding for Concierge Class:
We have our first Celebrity cruise in a couple weeks in a Concierge Class stateroom. I was concerned about missing the embarkation day lunch (one of the Concierge Class perks) because -- even though I checked in within hours of check-in becoming available -- we ended up with a 1:00-1:30 embarkation time, because that was the earliest available. With that embarkation time, at best we might make it to the tail end of the lunch...
FWIW, I just got off the phone with Celebrity's help line and was assured that regardless of our scheduled embarkation time, we will be allowed to embark early, so as not to miss it the embarkation day lunch.
If what the agent told me turns out to be true, it sounds like even though early embarkation is not listed as an official Concierge Class perk, it is apparently a de-facto perk because of the lunch.