StephVE has a point, the point being you are using the same characters, not just the same names. The characters are the intellectual property of their creator, the names can be in the commons, unless they are unique. Hard to write "THX-1138" and claim that is just some name you made up, for example.

I have two series with the MC name "Suki", but she is not based on any real person nor any prior work. Two people who worked on the first series with me wrote fan fiction using my main characters. I gave them permission to use them, without objection. A bit of a wrinkle there, my character developer and proof reader helped develop Suki. In my mind and heart, she owns that character too and I do not object to her using it online as her handle.

Anyway, the legalities disagree with me, I am all for being able to write fan fiction, while crediting the creator, without penalty. If someone does that from my stories, I am cool with it. My understanding is, legally, stay away from characters others created unless they give you express permission to use them.

My WIP uses common names and it would be a little difficult for any of the authors who wrote about Sarah or Nancy to honestly claim that I am ripping their work.