Being 2 seperate buddy passes, I'm thinking you'll need to check-in in ATL, but I may be wrong.

Anyway, I believe its concourse A, theres a small bank of kiosks, maybe 4-6 where you can check-in without exiting security. Also, theres a counter in A where the center meets the concourse, like near A18-20, I'm sure they could check you in as well.

Enjoy the trip, and lets have a report.