Hallo Karen,
Its interesting for me that an uncle of your gg-grandfather ROESLER was a ships Captain.
Now, the stepfather of my g-grandmother Wilhelmine JOSEPH was a Heinrich ROESLER/RÖSLER (b. ???, d. 1927). Wilhelmine herself married into a barge-owner family with ships in Brandenburg and in East-Prussia.
Anything of it familiar to you?
Kind regards,
Christoph Haupt