I think a few pieces might be clicking into place. I have the following in my files:
Gray, P. L. (Patrick Leopoldo), Gray's Doniphan County history: A record of the happenings of half a hundred years., Bendena, Kan.: The Roycroft Press, 1905., http://skyways.lib.ks.us/genweb/archives/doniphan/history/1905/2-4.htmlhttp://skyways.lib.ks.us/genweb/archives/doniphan/history/1905/2-4.html.
"Major Daniel Vanderslice was of Holland descent, and the spelling of his name was perhaps Van der Slice. His ancestors were among the early Dutch settlers of America. He was born at Reading, Berks County, Pa., on the 10th of February, 1799. His father, whose name was also Daniel, with his family, resided in Philadelphia, but owing to the prevalence of yellow fever in that city, in the fall of 1798, with which he was himself attacked, he sent his wife to Reading, to her father's, Abraham Cremmens, where she remained for some time after the birth of the subject of this sketch. His mother, on account of illness, not being able to nurse him, he was taken to a married sister, named Fox, who had lost an infant a few days before. When his mother recovered she returned to Philadelphia, leaving the baby with her sister, who had become so much attached to him that she was unwilling to part with him. He remained until he was about four years old, when he was taken to the family in the city. As Mrs. Fox and her family converse almost wholly in German, the boy had no knowledge of the English language when he reached Philadelphia; but as soon as he was old enough, he was sent to school and soon forgot his German.
His father died about the beginning of the war of 1812. That war had caused a vast amount of excitement; and the capture of many ships by American privateers and the naval operation generally, created a strong desire among the young men and boys to enter the service. Among them, young Vanderslice sought service on one of the gunboats that was being hurredly repaired, and which was soon after captured by a British squadron by the capes of Deleware. But Daniel had been prevented from going by his mother sending him up to Chester County, on Brandy Creek, where he was apprenticed to Joseph to learn paper making, with whom he worked out his time and became a skilled workman...
The article is longer, but this portion clarifies the relationship between the Cremmen/Clemmons family and the Vanderslice and Fuchs/Fox families. Elizabeth was Margaret's sister and Abraham Cremmens/Clemmens was their father.
I think I've had Daniel Vanderslices children attached to the wrong wives. Here's SWP's comment about Daniel:
"b. 6 p.m.Feb. 17, 1759...Wigmaker on 5th street below Race, Phila.By his first wife he had Catherine, Joseph and Abbe. By his third wife he had Daniel, Thomas, John, Mary.He was a sergt. in the 9th Penna Regt. from 1777 to 1780 and was discharged about Ap. 1, 1780."
The history I've cited above makes it pretty clear that Daniel (the younger) was a child by Margaret Clemmens, and that she had a sister who married a Fuchs/Fox. I previously had Margaret listed as the first wife, but I now believe she was the third wife. I'm tentatively listing the second wife of Daniel Vanderslice, whom he married in 1793, as Catherine Schunk. SWP listed no children by the second wife. The baptism of Marie VanderSleis, dau of Daniel and Margrete, born 9/10/1797, was probably the Mary listed by SWP for Daniel and Margaret Clemmens Vanderslice. The fact that John Fuchs and his wife Elizabeth (Margaret's sister) were the sponsors supports this conclusion.