A Pennsylvania death certificate after 1906 for one of these siblings should give the names of the parents.
My guess is that Hannah is their mother and she remarried Jacob HUMPHREY after the death of their father based on the age discrepancy of Jacob and Hannah.
Additionally I would give consideration to the following family in the 1860 census in Mifflin Boro, Juniata County, PA.The name is indexed as STUTS at Heritage Quest Online and all were born in Pennsylvania.
Joseph Stuts 35 Hannah Stuts 33 Henry L Stuts 9 George Stuts 5 Marth A Stuts 3
I recognize that this possibility has Henry L and not William L but the George and Martha (although different middle initial) are reasonable matches and Hannah's age matches the 1880 Hannah HUMPHREY.
Certainly Juniata County seems to be the first place to look for your family.