I'm guessing you are confusing fans theories? Since awhile back the mangaka revealed that there were two sisters from the mothers in the series and fans started making theories about who it could be and one of the most popular ones were that shinichi and kaitou's mothers were sisters. However its been revealed who the two sisters were, I won't say who they were in case you don't know but Kaito and shinichi aren't cousins.
Ah I see tyy ^-^
I'm on the latest Episode from it, maybe I missed some details, did they reveal it already in the Anime? 0.0
I don't think it's been revealed and spilled out clearly yet in the anime but you can pretty much conclude it from what was shown so far in the series.
Its cute and I like the ship, but I always had in mind they were cousins xD Idk if its like this, I do forget some infos in 980 episodes, but i think there was once a reveal xD