You probably already know all this, but I would take any family tree information on Family Search with a grain of salt. Especially so on Ancestry. That's just a suggestion as to what is the truth. Look at the original sources wherever possible (I can't see the Ancestry source you give).
In German tradition, Johann George would quite often go by George in common usage, but Johann/John would be a possibility. Henry Wilhelm would be a different person entirely unless something really unusual happened.
The German names Heinrich, Wilhelm, and Johann would be anglicized as Henry, William, and John, respectively.
Also, the 'th' sound in German isn't pronounced like it is in English, so an English-speaking census taker could easily write down Amulth as Amulde.