Have you tried to contact this person:
"Hello Cousin! I am also a great great granddaughter of his! My father is David Morely Otto, grandfather is Carl Eugene Otto, great grandfather is George M. Otto - one of John H. Otto's youngest children! I only know of George, Rosa, and August, but there were nine total children. Do you know the others? John was born in Prussia, but WHERE in Prussia? His father was named Joseph.
Please contact me! I am so excited to share! My family has a copy of John's entire diary from the civil war, as well as his sword. (it now belongs to my brother: Jon H Otto)"
Chris - firstname.lastname@example.org
This is correspondence from the message board which can be found under the header "John Henry Otto".