I am working on the Isaak line too. The Gottlieb Isaak I have was married to Louisa Schulz in Kulm, Bessarabia, Russia. I have an autobiography written by him for their 50th wedding anniversary.
I dont have any documentation of his brother and father and grandfather, but info I have from an aunt says that his brother John came to US before Gottlieb did. Gottlieb's father is Karl Isaak forn in Pabiantz, Poland, died in Kulm, Bessarabia before 1861. Karl's father Is Andreas Isaak, born Pabiantz, Poland 1759.
Like I said, I am not sure past Gottlieb, but if you have info that ties this together, I would appreciate hearing from you...