It could also be shock value to them, that they aren't thinking clearly. If someone showed me video or photo evidence of someone i know committing crimes, i wouldn't question if he's really doing them. I'd probably assume the video was real.
That said, you would still have to question HOW he got them and WHY he waited. Though time wise, we can't question it too much. Time is moving super slow. it's the 3rd year anniversary for us, sure, but for them, it's only been like 2 months or so. Hunter hasn't been "sitting" on this evidence all that long.
How is the one that would probably free Sterling from suspicion. How did Hunter magically have cameras in all the right places and if they are watching Sterling, the girls have to think that they too were being watched this entire time.