William Carl Burkhart (brother of your great grandfather, George Burkhart) is my great grandfather.
Their father's full name was Johann Freidrich Wilhelm (William) Burkhart. I also have the names of his parents and siblings. He married Anna Eberhardina Landgraff, daughter of Georg Landgraf. I believe her mother's maidne name was Seifert.
William Carl Burkhart married Louise A. Rathsack in Manitowoc, Wisconsin. Their children were Leslie Herman, Charles Louis, Esther, Elizabeth Lucille (Libby), Walter John, Frederick Charles (my grandfather) & Irwin Clyde.
I'd be happy to share my info with you. Of course, I have a lot on William Carl and his descendants, as this is my direct line.
I also have quite a bit of info. on William & Anna's son, Charles, and his descendants, as well as some of the other siblings.