Barbara, you are right that Ernest's name was Sterzer, not Herzer as I had previously read it. In fact, the Hungarian genealogical website Radix confirms the Sterzer name in Süttő.
However, he was not traveling with two nieces, but niece and nephew. Look at the manifest again and you will see that Johann (German form of John) is a male.
It is possible that Ernest returned to Hungary (many did) after accompanying his niece and nephew to their family, or that he changed his name after he immigrated. If he returned to Hungary, you might find him listed in the death records for Süttő.
Is there some reason you are avoiding looking at the Süttő church records? Do you need help?