Adobe After Effects. Clean up Greenscreen Videos (rough), trim to fit, composite your work into final video

I have 7 people that have been filmed against an average greenscreen. I need to isolate their heads for insertion into a movie clip. See sample quality....not a professional greenscreen setup, so a bit extra work will be required extracting characters from their background. The seven peoples heads you will be isolating need to fit onto a cartoon body in a video clip that will be provided to you. a draft of the final product has been included to show you what we are looking for. Task required: 1. isolate the heads of people from greenscreen background to create 7 x 3 second movie clips (base clips will be provided) 2. clean up the heads around the neck area to they fit onto the cartoon drawings (background movie-also provided) 3. position heads into the 3 second movie clip The final result will be a 3 second movie clip with 7 real peoples heads overlaid on cartoon character bodies.