Did you use Final Cut Pro to pull the key? Your problem is caused by the key not being clean enough. It could be a simple fix or it could be very fiddly depending on how well-lit the background is and how dissimilar it is to the subjects.
I’ve done similar things in the past and found one of the best options was to key using the Color FX room in Apple Color and then boost everything until the selection goes pure white.
Another option is After Effects. Roughly cut around your subjects using the pen tool, then use one of the many chroma/luma keyers to pull the key. Thanks to the masking you only have to key out the kits left inside the mask after cutting around the subjects.
Let me know if you need me to expand on either of those suggestions. I didn’t want to go into too much detail in case they’re what you’re already doing. Bottom line is you need to key out the white better.
Alex Elkins
Twitter: @postbluetv
http://www.postblue.tv
Post Blue showreel
Latest work: Greyhounds in Motion at 500fps
My Vimeo Pro page