Hello there, are you still on this search?
I live in Perry County and descend from John Jacob Umholtz through his son William Henry Washington.
I can say that Michael Umholtz's grave in Millertown is a misprint or the headstone is missing. His daughter Rebecca Holtzapple's grave is there.
His son's, Michael Umholtz, father of John Jacob, grave is in Juniata County. Many of his children are buried in the graveyards west of Port Royal.