just in Moment I read your question.
I looked at information about surname Momm or Mumm from Schleswig-Holstein. In my documents (state documents) there is the name Momm sometimes written Mumm (but more often Momm and my living ancestors said Momm is the right form.
In an old document from 1908, in which different information about the married couple are inside I found one commentar to a Claus Momm.
Markus Momm was born 26.03.1850 and (getauft - in church) 21.04.1850 and he had 3 Gevattern . one was Claus Momm.
Gevattern is an very old german word. So I know is something like a related, but can be a near friend) here I believe it could be a brother of the father of Markus Momm who was the Gevatter when Marcus was baptism. ( The baptism document is stored in Taufregister der Gemeinde Wilster, Probstei Wunsdorf Nr. 20. But this are official document infos of 1908. so the Taufregister is nowadays may be in another church register.
Greetings Regina Haase