Can you get pictures of their stomachs? From above, it's impossible to tell if they're self, irish, or berkshires.
Chu: Alibno dumbo, like you said.
Mordichai: He seems like a cocoa or mink hooded. (See: http://www.afrma.org/ratselfs.htm#chocrat )
Serenity: Agouti rex.
Firefly: Black
Rigby: Black rex
When breeding them, you will get mostly albinos, black and agoutis. I personally would breed Chu and Serenity to Rigby and try to get some double rexes, and some dumbo rexes. Depending on what genetics Chu is hiding, they can have albinos, blacks, ect. Albino hides the true color of the rat, so without knowing their genetics, there's no telling what may pop up. Breeding Serenity and Rigby would give you all agoutis and blacks.