a friend of mine has Bahnsens in his family. His mothers maiden name was Bahnsen. The family is located in Kiel/Schlewig-Holstein.
If you are interested I can ask him to find out more.
Btw. I think the name Sanky is wrong. Could it be that it means Sönke and Christina? Sönke was and is a popular name in nothern Germany.
Greetings from Germany