Pleased to make your acquaintance!!You are my third cousin twice removed, but then I've got a half-century on you age-wise.I knew about your half-siblings, but not about you & your brother.
I can send you a 7-page chart generated by my genealogy software that depicts the Seyffert males from the 1854 immigration to the present, as I knew them.[You can find my email address by simply Googling my name, if it doesn't display.]I don't mean to slight the women in the family, but the goal of this chart is to make clear which of the Seyfferts you might encounter somewhere are "kin," and which are not -- at least not from any American relationships.And the women don't generally pass on the name to the next generation.
But there's the possibility of relating to others through ties back in Germany.There are Seyfferts in Ontario that are related to VA-NC Seyfferts, and they all had relatives in NM until the name died out there.And then there are TX-CO Seyfferts, Chicago Seyfferts, New York Seyfferts, Massachusetts Seyfferts -- and who knows how any of them relate to us or to any of the others??