Yes, Nancy Black did have a brother Jonathan (no birthdate)
About James Black, will proved 12 January 1809, Juniata Twp., Cumberland County, PA. No mention of Wife.Sons:John, William, James, Jonathan, and George.Daughters:Mary, Jane, Rebecca, Abigail, Sally, and Nancy.
The will of John Black Sr. of Tyrone Twp. Cumberland Co. PA also shows a son, Jonathan.No birthdate, but will proved 28 September 1790.
I am still looking for the parents of Maria (Mary) Black who married George ZINN in 1822, Cumberland Co., PA.James Black is a possibility but no proof.