Hello Sandra, some weeks ago I started researching my family roots. My Grandfather was Herbert Marquardt, born 15.05.1903 in Vandsburg. He married Charlotte (Siegfried) and had 6 Children. His parents are:Eduard Marquardt b. 28.01.1861 in Vandsburg Abbau d. 22.01.1919, married w/ Emilie (Moddelmog) b. 30.11.1871 in Schmilowo near Vandsburg.
I am not sure, if this is the Marquardt line you are looking for, but this is what I found out, up to now. Honestly, I am not absolutely sure about the correct dates. That has to be verified next time.
I would very much appreciate, if you can reply to this post - positive or negative.