I have a 3rd ggf Joseph Helwig from Irmtraut, Germany (in the Westerwald area) whose genealogy I am just beginning to research. I will watch for a connection to your William and David Helwig. My Joseph was born March 22, 1825. His wife was Marie Charlotte Witt. He immigrated to the USA in 1868 prior to which he was living in Gutzkow, Germany (north of Berlin).
If you have other extensive Helwig family info, I'd appreciate hearing from you.