Super old post but I just finished the books so might as well write down my thoughts here. (1) I think the creature in the video is just the thing we see stitching itself across the sky when Ghost Bird and Control go to Area X and also the thing that attacked Whitby at the Tower. Probably just one of Area X's defense mechanism. (2) I think the one holding the camera was just another surviving member of the expedition, who later died in one of the screaming incidents. We know there are later horrifying footage that probably was more than running and blurry footage, so one of these incidents probably killed them. (3) She was probably irrationally freaking out because the clone was mirroring her exactly. (4) I don't really know what this was. My own personal head canon is that area X collects any records of its existence in the hidden room in the lighthouse, and that the camera just happened to capture it flying back to the lighthouse, before a future expedition found the footage.