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You could use a curves effect to boost the contrast and turn that footage into something close to a black-white mask around each dancer, assuming they stay in front of the lit areas. Add a hue/saturation effect with sat -100 to make the whites neutral. You're only interested in getting pure white around the edges of the figures and pure black inside, not turning the entire stage white.
You'll then need to mask around each dancer so that all the unwanted areas are removed, and probably keyframe the masks to follow them. Put a solid white layer below to fill in the unmasked regions and you have a silhouette.
The floor looks to be too dark to pull the edges out automatically using this technique. It *might* be possible but you'd need to treat the floor and the wall sections separately, merging them back together with a mask. However from that photo it's looking like the floor will be a rotoscoping job.
Still working on this ginsiv? Let us know if you need help.