Less detailed people/silhouettes is what I did for mine as well (don't have time to crop the panels ._. ):
During the sketch phase, I copied and pasted people around and then I made small adjustments during inking and gave them different tones. I think one or two people I copy pasta'd and just flipped.
In the third panel, I drew a few people, but didn't put in their faces which also helps the main characters stand out. Then the back is just some silhouettes made with comic tones.