Wdym…it was literally Reiju and Ichiji
No, the two shadowy figures appeared on Cacao Island
Reiju/Ichiji are on WCI & they were spotted by Brulee who told Cracker
Not only the time frame doesn't match, but Reiju & Ichiji have no reason to stop at Cacao Island
They can fly directly to WCI & it's not like they don't know the place
And finally why would Oda draw Reiju/Ichiji in the Castle, draw them when Brulee spotted them & when they save their Siblings on WCI
But hide them in Cacao Island?
It's pretty obvious that the shadowy figures are still not shown & they will meet with Vinsmokes on their way out which will most probably be the focus story of this Cover Arc