The II part (or jr) refers to his fore names, not his surname. All it means is that his father was called John Henry Hempel. His wife would only take the Hempel part.
The reason Vanilli's profile shows the II in her (married) surname is that it is listed in her Current Last Name field. Just go in and edit that field to correct her name display! The II is not part of her - or her husband's - surname.