Nancy Brown's brother, Arthur, Jr., said she was married to John Newman in his 1845 application to get his mother's widow's pension (presumably as whatever she'd been entitled to would accrue to her estate). I'd say a brother was a pretty reliable informant on such a question.
Jacob Newman is not part of my direct line but I've looked over a number of his records and haven't ever seen a Nancy mentioned. He was married to Mary Ann Royal, granddaughter of Owen Royal - in 1832 she and Jacob sold 90 acres to Ollen Royal that were described as "being the third part or lot of the lands of Owen Royal Decd." Owen's will, written in 1820, named as legatees the sons and daughters of his sons William, Labon, John and Biggars Royal, so Mary Ann was obviously the daughter of one of them.
Jacob may have had other marriages, or so I've heard other family researchers say, but I haven't seen evidence of that so far. But I haven't done in-depth research on him, either, so could be wrong.
I have the wills of Arthur Brown, Edward Brown and Robert Butler, among others. Sometimes trying to untangle the generations, in light of the recurring given names, can be a real challenge, though!
Thanks for your response.