Originally Posted by Global321

Assuming you are OW Emerald on another airline (not AA), yes you can use Flagship Checkin.

You can use Flagship® First Check-In if you’re flying on any flight operated by American (regardless of
cabin
).*

*American Airlines AAdvantage Executive Platinum customers traveling solely on North American itineraries do not qualify for Flagship® First Check-In access. North America is defined as the United States (including Hawaii and Alaska), Canada, Mexico (except MEX), Bermuda, the Bahamas and the Caribbean.

If the others are on your ITN they will have access too. If they are on another ITN (even same flight), by the rules, no they will not have access. However, in practice, there are many reports of everyone using Flagship Check-in. YMMV