I have found the answer to your questions about Phillipus Jacobus Isenberg, son of Gabriel Isenberg. There's a pretty complete account of him that I found going through my Family Tree Maker software that will hunt for anybody online. But the name was misspelled - it was ICenberg. The material came from Ancestry's One World Tree. It says that he died in 1823 in Springfield, Clark Co., Ohio.
His marriage to Anna Maria Haspelhorn was on 5 Feb. 1788.
It did list another spouse also, but gave no date of marriage - Margarettia Hospeliiorn (Misspelled Hospelhorn?).
I'm thinking this is the sister of Anna Maria who probably married him when Anna Maria died.
Children's names (but it does not say which belong to which mother): Magdalena Isenbarger; Johannes Isenberg; Henry Isenbarger; Gabriel C. Icenbarger; Susanne Isenberg; Catharine Isenberg; Mary Isenberg; Jacob Isenberg; George Isenberg; John Iscenbarger.
I cannot tell you if this is correct or not. All I have is Phillipus' name, date and place of birth. Hope this helps!
Nancy M. Goodwin email@example.com