hey there....
The first two photos appear to me to be Astrea snails. The forth looks to be a Cerith snail. Both harmless....
The third photo, on the other hand, looks suspiciously like a Heliacus snail....a predator of soft coral polyps. Hard to tell from just the shell, they are pretty similar in appearence to many small astrea species...if you get one live, flip it over and see if it has a "trap door" that covers the entrance to the shell and protects the animal. If so, it is likely a Heliacus snail...
MikeS