Works created on or after January 1, 1978 or works created before that date but not registered with the Copyright Office or published is automatically protected by copyright from the moment of creation for the life of the author plus 70 years. So while your father may not have registered his photos with the Copyright Office, they may still be protected by copyright already. If this is the case, then copyright may be transfered by will or intestate succession statute (where there was no will). If your father's will gave the photos to his widow or if he died without a will, then to transfer the exclusive rights to the photos to you, the widow would need to sign an agreement in writing to transfer the copyright to you. You may then record the transfer with the Copyright Office, which is not required but can be advantageous if you ever have to enforce the copyright against a thrid party. The agreement to transfer a copyright is governed by state law so I recommend getting a North Carolina lawyer to draft an agreement.
If you are going to sell the photos to the public, then there is a mandatory requirement to deposit (file) 2 physical copies of the work with the Copyright Office within 3 months of the first publication (offer to sell to the public). While you do not have to officially register the copyright with the Copyright Office, it may be helpful legally if there is an issue with the photographs or the copyright.
The good news are: copyright survives the creator. How long? depending of when were the photos were created. You must ascertain the date of creation before you can know how many years would copyright attach.
Next you must make sure that you have inherited the property. Your step mother giving you the photographs is not enough, you must have title. Somebody needs to review who has the rights, siblings, widow, family, etc, before you can use the photos. Actually if you use the photos without authorization you will be potentially violating somebody's copyright. Check with an attorney.
If you simply want to sell the photographs you have in your possession you can lawfully do so w/o worrying at all about copyright or stepping on anyone else's rights. Just sell them.
BUT --- if you want to make copies of the photographs and then sell those copies then you need to determine who owns the copyright in each of the photographs. If your Dad was the photographer but did not identify in his will [or trust] who was to own his copyrights [or if he did not have a will at all] then the copyright in each of the photographs belongs half to his widow [even if remarried] and the other half is split equally among his children and grandchildren who were alive at the time of his death.
NOTE 1: this is the way it works under California law. The division may be different under the law of the state where your Dad was living when he passed away.
NOTE 2: if any of the photographs were created before 1978 and then "published," under some circumstances the copyright in those published photographs may have terminated. Which means that those are now in the public domain. Which means you can freely copy and sell them. For those that were not "published" -- regardless of when they were created -- then their copyrights last for another 55 years [70 years after your Dad's death].
NOTE 3: Because you're a "joint owner" of the copyright in the photographs that your Dad took you may lawfully copy them and sell the copies. If you do, however, you must share what you earn equally with each of your co-owners. You may not sell the copyright in any of the photographs or grant anyone an exclusive license to use the copyright in any of the photographs.
If your Dad was not the photographer but simply collected the photographs, then you cannot copy the photographs UNLESS you get permission from the owner of the copyright of the photograph or if the photograph entered the public domain.