The contact for the families from Ivanack and Anklam is Diana Kieffer-Stavenhagen, Sachsische Str. 6, 10707 Berlin, Germany. She collects information on all branches and coordinates the bi-annual Stavenhagen Reunion in Stavenhagen, Germany. If your family has Jewish roots (or hails from Alt-Strelitz) then I am the one who has been designated (by default) to have collect that information.
It is best to write to Diana in German. She does speak and write English but it is easier for her to share her information in German.