Edgar is called the oldest of the six Planck siblings - three boys (= Edgar, Clarence, Roy) and three girls.
The biography states Edgar was born in LaGrange County, Indiana in 1869.
Christian is the son of John and Magdalena (Yoder) Planck (per the Sons of the American Revolution records posted by T. Kerwin). The family seems to be living in St. Joseph County, Michigan, in 1860, is that right? One of the sisters to Christian could be mother to Fred Roof - is that what you are suggesting as a possibility? I suppose the same could be said of Emma's sisters...
1860 census John Planck 43 Magdalena 41 Rebecca19 Christian 18 Mary16 John 13 Samuel12 Joseph10 Susanna7 Magdalena1