I hope this message finds you well, present circumstances excluded. I am sorry for your loss. I am a licensed IP attorney with over a decade of legal experience handling matters of this nature. It is a pleasure to assist you today.
First things first, the artwork was copyrighted at common law from the moment he created it. These common law rights divest to his statutory heirs (you guys) automatically at his death. That is good and should allow you to rest a little easier in the end.
That said, you do need to file this work in the federal system with the US Copyright Office. This can be done once the probate is complete. By being a 50% owner, you still have 100% rights to file for copyright protection of the works. Your wife will have the same rights as well and even if she does not file, will still be allowed to license the works. That is the unfortunate nature of bifurcated ownership of IP.
Point being, when you have the probate order issued, you can then file for Copyright protection...however, I would hesitate to file before the probate order is issued. You technically can file as you sit her today by statutory inheritance of this common law rights to the IP. That said, it is cleaner (certainly if litigation occurs down the line) to wait until the probate is complete.
Wayne, let me know if you have any other questions or comments. I want you to be as comfortable as possible as you move forward with this issue.
Please also rate my answer positively (three or more stars) so I can receive credit for my response.
Best wishes going forward!