Halloween
Possibly the kids, since they are after all the Rebel Black Dot Society, a cohesive group, could all share a common theme. You see, the problem with horrible theme costumes is not that they are themed, but that the horrible people selecting the themes make horrible decisions. An example: boyfriends and girlfriends going as T-Birds and Pink Ladies from fucking Grease. (Anything Grease related is clearly a terrible idea.) On the other hand, two people (not one, not three) are required to go as Joliet Jake and Elwood, the Blues Brothers.

Excellent costumes for couples include (but are not limited to): Nick and Nora Charles (the classic), Han Solo and Princess Leia, Margot and Richie Tenenbaum, Sid and Nancy, or Tyler Durden and Marla Singer.

Excellent costumes for groups include (but are not limited to): the Blue Monday kids, the Hopeless-Savages, the Justice League of America, the Reagan Administration, or the cast of Cheers.

The Rebel Black Dot Society might go as...
The Big O
Roger Smith (Parker Peppard)
R. Dorothy Wayneright (Margaret Eastman)
Norman Burg (Scipio Winter)
Angel (Mary Peppard)
Major Dan Dastun (?)
Schwarzwald (Pete Foster)
...we need one more girl character for Stacy Fahrenheit, but I'd rather avoid Vera Ronstadt

Blue Monday
Bleu Flanigan (Margaret Eastman)
Clover Connelly (Mary Peppard)
Victor Gomez (Parker Peppard)
Alan Walsh (Pete Foster)
Erin O'Neill (Stacy Fahrenheit)
Mr. Bishop (Scipio Winter) ...he'd be better as Mr. Bishop than as Monkeyboy

Hopeless Savages
Zero Hopeless-Savage (Margaret Eastman)
Rat Hopeless-Savage (Scipio Winter)
Arsenal Hopeless-Savage (Mary Peppard)
Twitch Hopeless-Savage (Pete Foster)
Dirk Hopeless (Parker Peppard)
Nikki Savage (Stacy Fahrenheit)

Teen Titans (Cartoon Network version)
Robin (Parker Peppard)
Starfire (Mary Peppard)
Cyborg (Pete Foster)
Raven (Stacy Fahrenheit)
Beast Boy (Scipio Winter)
Terra (Margaret Eastman)