I'd like to know the basis of the contention that Carl Lavien came from Lübeck, because it doesn't make sense that he would travel inland 120 miles to Minden to begin his waterborne journey, when Lubeck is a seaport in its own right. More sensible is the town name I found on his later US Passport application, in which he stated his birthplace as "County [Kreis]Lübbeke". This is an inland town only ~10 miles from Minden and connected to it by a tributary river. I found several other contemporary instances of his spelling associated closely with Minden and Rahden, which are both very near modern Lübbecke. This makes the Minden-Bremen water connection far more comfortable for me: is this what your post intended? If so, we should be looking in the Minden-Lübbecke district for our other distant family, not to the northeast of Hamburg as I understood.
Other question: where did you get this narrative?