Until we have some official verification regarding Joy and Ninjoy, please refrain from linking the two on the character pages. The character pages have to be factual and should not have any, or any hints of, speculative or fan-fiction elements. That's why I removed the sentence "Not to be confused with Ninjoy" and your trivium regarding similarities in hair and names.
But how does mentioning similarities parallel to mentioning any speculative thoughts of them being related, the same person, or anything else along those lines? I understand refraining from blatantly stating that they could be the same person or related. As for the "not to be confused with" statement, the names are very similar and can be confused with. Would that be the reader's fault for mixing them up?
Even linking the two together, considering how they appear similar, and share a base name, can lead to speculation in the mind of the reader. The similarities are not oblivious to fans as I have seen way too much excitement over the possibility of Ninjoy being Joy's alter ego.
As of now, I would prefer not to connect the two at all on either of their articles (Joy or Ninjoy). Flipline says that Joy is a BRAND NEW CHARACTER, so her page should just say that for now. They didn't lay hints that there is something about her, and if they did, those hints would most certainly be allowed.
Our job as editors on this specific wikia is not to allow readers to mix them up in the first place. The articles should remain unbiased, factual, and free of speculation. Everywhere else...speculate away. That's all I'm saying.
And if, in fact, it does turn out that Ninjoy and Joy are one and the same, I will have no problems with people writing as such in the articles.