> I thought we had an amendment that said that while we might be compelled to show up as a witness at court, we can't be compelled to testify if we think it might implicate ourselves?

It only protects you from being compelled to be a witness against yourself; because of indirect use, you can refuse testimony that isn't directly against yourself based on that protection, but only so long as you haven't been granted immunity that protects you against those derivative uses.