i have a couple in mind for sweet tooth..
small brawl kid sweet tooth outfit would be like this but keep his mask and flames the way they are.
another could be his default pants with a stray jacket on instead of no shirt and harness.
another one could be his pants with an ice cream drivers shirt like in his 2012 intro movie.
the last one i have is a bit of a stretch and very unlikely but maybe a sophie kane or a marcus kane as a alternate
sophie kane is his daughter who took her own life in fear sweet tooth would find and kill her... etc etc.. calypso rivives sophie with a sweet tooth mask he made so she can kill for him.
marcus kane is from older games but he is just the normal looking man before sweet tooth takes over.
Sackboy (Console Kitty from LBP2)
Spike (Star shirt and all red hair from Ape Escape 2)
Raiden (Gray Fox ninja from MGS)
Ratchet (Mustachio Furioso from Ratchet & Clank Future)
Jak (Jak facecoverd scarf from Jak II)
Sweet Tooth (Clown costume from Twisted Metal 2)
Heihachi (Classic alternative outfit from Tekken series)
Sly (Ninja costume from Sly 4)
Drake (Baseball shirt Drake from Uncharted 1)
For Kat, only the 'Dark Cat' is pretty much confirmed, it was the most popular costume of the five aside from her normal by quite a large marigin.
Other than that, its a decision between the Maid, the Spy, and the Schoolgirl. Most likely its going to be the Spy, but its open to possibility. It might even be Raven for all we know.
I'm surprised nobody's talking about colors. I could probably Photoshop up some concepts on what I personally want for Kat, such as a Raven color (pale skin, black hair, black clothes, red trim).