you are right, of course, BUT the unbreakable #1 rule that I established when starting this project 3 years ago, was that unless I had a source saying something was wrong, I do NOT remove it.
The Midrash DOES tell us that Keturah and Hagar are the same person, and we DO know, that Keturah DID have additional children with Abraham, so we might actually have a source for this.
I wasn't party to your unbreakable #1 rule or why it was put in place. But if that is the rule, then anyone can create fictitious people anywhere, and no-one can prove them wrong. In almost all cases, it is likely to be impossible to prove that someone never existed. In other projects, people are being removed / delinked because there is no source that they ever existed, so why is the Biblical project any different?
I am well aware of Midrash that Keturah = Hagar. But I have never come across a source for an additional sister - Midrashic or otherwise.
I would suggest a curator's message to the profile manager asking for a source. If there is no source, I cannot see a reason to retain this.