They’re the same. Usually, when I do one of these this v. that things, the two words are not the same. In this case, they are interchangeable.
Sort of. (You knew it couldn’t be that easy, right?) Amongst is very commonly used throughout the British empire and Canada, probably some other places, too. In the United States, it is very rarely used. It’s considered almost archaic. We say among.
Generally, those who use amongst were either taught to do so, for whatever reason, or are trying to sound educated and erudite. They may actually be educated and erudite. That’s the trouble with vocabulary. Knowing the word is not enough. You have to know how to use it.