What’s going on if there’s a different personality in my mind that I can talk to and that shares my memories, and he identifies with the name/pronouns of a fictional character, but the two of us are also kin for different fictional characters simultaneously? Do I have DID and am fictionkin, or am I just fictionkin for all three characters and I like talking to myself? I feel like a liar, even though I’m probably not…

This is definitely a question I can answer! Lets break this down!

there’s a different personality in my mind that I can talk to and that shares my memories, and he identifies with the name/pronouns of a fictional character

That’s a headmate. A fictive headmate specifically. Possibly a soulbond.

but the two of us are also kin for different fictional characters simultaneously?

Simple. Your headmate is kin, and you are also kin. You are two separate people with separate kinselves.

Do I have DID and am fictionkin,

You are fictionkin and on the multiple spectrum. Multiples do not always have DID.

am I just fictionkin for all three characters and I like talking to myself?

Sounds like you have a legitimate headmate. You are only kin with one character, and your headmate is kin with another.

I feel like a liar, even though I’m probably not…

No need to feel like a liar, this is a perfectly typical experience for multiples who are also fictionkin.