I just came across your 2002 bulletin-board about the Ott-Bessinger family. I can't help with the early history of these families, (though my records for your greatgrandmother's siblings are not totally in agreement with yours), but I do know a bit more about the later history. My wife, Marlene Maser, born in Au Gres, MI, is Mathilda Firchau's granddaughter, and Philip Ott was her step-grandfather.
Of the Ott children you listed, I believe that Julius, Gottlieb, Philip, Rosina, Friedlinde (Frieda) and Martha were by Philip's first wife Maria (or Mary), and Adolph, William, Carl and Emma by Mathilda Firchau. Mathilda also had children Julius, Rosella and Martha by her first husband, Edward Retzloff; they were, I believe, adopted by Philip Ott.