Ethics of dead characters

So this is a bit of an "Ask the Ethicist" post. So, Me and a close friend (which I will refer to as A) had a big and stupid falling out a few days ago. We used to Rp and even made up some characters, those being the Horsemorph characters as seen on my Deviantart page. We came up with them a little over a year ago out of my desire for a few predator characters, and A's desire for transformations from human to animal. We both liked the idea of horses and went with that. I had the idea and created the colors and personalities of the characters, and A gave them names that I agreed on. We added on a few characters later in the same fashion of me making the personality and physical appearance, and A giving them names, which was always a sticking point for me (although I did name a few). We also created some side characters. We had created many different story ideas and storylines for them, and I was going to write stories about them in a series (as evidenced by the character sheet) I even had a character in progress, Angela. Mr. A also drew a 2 pics of one of the female characters, Belinda, but stated on Deviant Art that she was called "Fun Mare" and may or may not be the same character (Likely not knowing A, but the physical appearance would look almost identical).

So here is my dilemma and question, Since A has no interest what so ever in using these characters as we used to (that being giantess and vore and play), is it right for me to claim them as solely mine? The alternative is I don't and the characters die. Suppose I write a story on them, could A sue me? Could I sue for the fan art? Yeah, I know it might seem silly as the characters weren't used outside of private Roleplay until recently, but they are my longest-running and most well developed characters. Losing them would be a massive waste.

If you both developed the characters, you should have the full right to use it, however, the same goes for him, I'd say. You cant claim them as solely yours thus, unless he gives up ownership of the characters. Of course, those characters become 2 different entities, if you both continue to use them.

Maybe you want to talk to him about it though, in case you dont want to upset each other accidentally (or intentionally.)

This is from an ethical standpoint.