May be irrelevant but I have a story that involves a Mrs von Stieglitz - possibly a Baroness. She may have lived at Carrickblacker House.
My grandmother was one of a family of 5 who were born in 1860s and lived at Hacknahay Portadown. The family was poor - their father was a weaver at home. The 5 children spent their summer evenings walking around the lanes in the area (According to my father who was born in 1912)They met and talked to Baroness von S and she appears to have decided that William John Neill was clever. According to my father the Baroness managed to arrange for William John to go to the local "grammar" school and then he got a scholarship to Trinity College Dublin. He was awarded a degree and then became a teacher in Belfast and Newtownards (not sure which was first)However sadly he died I think of pneumonia when he was in his thirties at his digs (boarding house) in Belfast. He was not married. This was a great disaster to the family as he was seen as the great hope! Three of his siblings did not marry and my granmother was the only one to marry - late in life - and surprise to everyone had my father her only child when she was in her forties.
I still have a few books that belonged to William John.
You are the first person I have ever heard of that had an interest of any sort in the von Stieglitz family!