I am not an expert on surnames and I always hesitate to try to define ethnic connections from a surname. For example, you might be researching the Kowalski family as a Polish person only to discover that at some point the family was actually Germanic with the surname Schmidt. Both translate to Smith. I have the surname Girschewski in my ancestry who were clearly German Lutherans yet most of the Girschewskis in the world are Polish Catholics. I have no idea why or how the Germans adapted or adopted this surname except a rumour that it might have origins in the name Gersch.
The Jonkeit and Gutzat families may have German ethnicity but the surnames (or at least the way they are spelled) almost seem to have a Lithuanian context.