As to discerning his New Jersey niece's political leanings, there is a book that may help you to understand this. The following is from Joe Bilby, posted to the NJ in the Civil War Discussion Board:

"I assume that by 'position', you mean political leanings. The best work on the subject of NJ politics leading up to, during and following the war is Dr. William Gillette's 'Jersey Blue', published by Rutgers University press. Gillette disposes of a number of commonly held assumptions about New Jersey."

I have not read this book, but I gather from this post that NJ was not the 100% pro-Union stronghold, which is the commonly held assumption.