Below is a list of new books that were reviewed in the 1868 Peterson Magazine's January issue. Each of these books were listed as a "New Book" however, I found some had earlier copyright dates. Also, being a January edition to see an 1867 date makes sense. I've attached links to as many of the books as possible for you to see what your characters might have been reading during those days. Enjoy!
The Guardian Angel by Oliver Wendell Holmes This volume is a later volume but the same book.
Shamrock & Thistle by Oliver Optic
Rienzi by Lord Lytton Google books has an earlier publishing date but I believe it comes from the text of the story not the actual publishing date since it was a new book in Peterson 1868.
Widow Spriggins, Mary Elmer and other sketches by Mrs. F. M. Whitaker (This book doesn't have a link in Google books or on the web but is mentioned in many publications.
A Book About Lawyers by J. C. Jefferson (Again no link in Google books or on the web.)
Silcole of Silcoles by Henry Kingsley
The Child's Own Book of Standard Fairy Tales
Circe or Three Acts in the life of an Artist by Babington White
Birds of Prey by Miss Braddon
Modern Palmistry by A. R. Craig M.A. (No link)
Malcolm's Cottage & Malcolm's Friend by Mrs. J. McNair Wright (no links but books are available by this author in Amazon)
Breaking Away by Oliver Optic
On the Wing by Nellie Eryster
The Child's Illustrated Book of Natural History by Duffield Ashmead (Not in Google's Free books but you still might be able to access it.)
It Isn't Right by Mrs. Joseph Lamb (This has an earlier publishing date than 1868 but it was listed in Peterson Magazine.
Crocked & Straight by Mrs. Maratha E. Berry (I was unable to find an online copy. You can pay to have a book printed of this title but all free copies are no longer available on the Internet.)
The Tenants of Malory by J. S. Le Fann