replicating a crowd takes a lot of patience haha. you need to do some rotoing, tracking, masking, positioning, adjust for distance, color correct, transorms, and warping for both lense distortion and environment angles. we did a little bit of crowd replictaion for a small commercial at the last tv station i worked at. pretty much just think of all of the steps i mentioned you can apply them for your footage. if you put the footage up in a place where i can access it i can try to walk you through it.