This Jacob id not the son of Rudolph Hannah (Siple) Kagy. Their son died in Fairfield Co in 1886 and was born on the early 1800s. Rudolph did have a brother, Jacob. perhaps this is your line. You may have this book at your local library: The Kagy Relationship in America. If not, you can probably get it on an interlibrary loan.
Researching Kagy, Crook, Hosler,Ream.