I can really only see the idols doing cosplay and it would most definitely be a group Halloween thing haha...maybe Deep Cut!! (Leticia is big man)

I honestly don't know, I think Grin would make a good Phantom of the Opera

Balei has cosplayed as Mirko from MHA but as for anyone else maybe Storm from Marvel v Capcom or Twili Midna!

Fausto would be Simon or Kamina from Gurren Lagann!

Cecils basically inspired by Beelzemon so that'd be a good start!

Jasmine: Miyamoto Musashi From Fate/go

Andres: either Vulcan from Fire Force or Jotaro Kujo From jojo

Jin: Chun Li...it was Mary's idea...