Please try without the marks first, see if the same thing is happening.
They will all 'wait for photographer' in front of the camera, the photographer sim will bend down quickly like he's taking a picture, then stand back up immediately and then just forever be 'taking a picture'. Then one of the Sims will queue up a task and leave, and the others will follow right after.
I've tried this multiple ways, in different locations, with different groups. It just won't happen for me without the marks first.