I have been trying to figure your Jacob and Maria out from the Siemens (1910) book and it appears that he was the son of Julius Siemens from Schoenwiese (Chortitza Colony - Mennonite) near the Dneiper River south of Kiev. He was a cousin to my husband's grandfather, Julius. My husband's grandfather also had a brother Jacob but the children's names aren't a fit. The Jacob, son of Julius (b. June 15, 1836), had Maria, Anna, Julius, Cornelius, Jacob, and Helena. The Cornelius isn't there but the book isn't always complete. If you want more information let me know. The ancestor who originally went to the Ukraine from Marienburg, Prussia was named Peter Siemens(1765-1845).