Rehearsal Dinner near Douglasville
Sorry don't know the immediate Douglasville area.
You are about 20-25 minutes from both Smyrna and College Park...without traffic...rehearsal dinner Friday night?...traffic will be worse on a Friday early evening.
In Smyrna, there is South City Kitchen and Muss and Turners...both can do BBQ, I'm sure but no spot for the band.
In College Park, you could try The Feed Store or The Pecan on Main St.
You are about 15 minutes away from Villa Rica where there is a golf resort called The Frog at The Georgian. I think they do events.
I know the driving is probably a concern, but you're only 30 minutes from Midtown (again the traffic could pose a problem). Many options there. Might be fun to get those "out of towners" into the city.