You have to add '2' to the second hider so that it looks like this
[hider = Hello]
Blah
[hider2 = Here is the second one]
Yep [/hider2]
[/hider]

Without the spaces it would look like this:
[hider=Hello]
Blah
[hider2=Here is the second one]
Yep [/hider2]
[/hider]