I am not sure how or if our Mahn lines are connected, though it is interesting that they both ended up in the Spokane area.This is how my line goes:
Paul Mahn, b.1833 Prussia Arthur C. Mahn, b. June 27, 1883 Alta, Iowa Vernon Mahn, b. March 2, 1908 Illinois Betty Mahn, b. December 26, 1928 Christine M. Richardson Terry Carpenter
I did a quick search of the 1930 census at Ancestry.com and found your Theodore and John in Montana.You may already know this, but it shows John's father's birthplace is Nebraska as is John's.I am assuming that the Paul Mahn I found living in Spokane in the 1930 census is John's father.This Paul was born in Nebraska and his parents were born in Germany.
The Paul Mahn that I have in my line (which is the same Paul Mahn you found at www.familysearch.com, born in 1874) was born in Illinois therefore I don't think they are the same Paul.Of course, this doesn't mean they aren't related in some way.
I am going to continue looking for a connection.Let me know if you find anything else.I will do the same.