Female fiddler crabs question!?

Ok, I have a 40 gal tank with guppies, 3 different kinds of tetras, albino and regular cherry barbs, panda platties, and 1 male flaming dwarf gouramiand and 1 female dwarf Gourami. I saw Fiddler crabs at petsmart and was thinking about getting some. But I use to have a male fiddler crab and if I would put him in my community tank i knew he woulda killed my fishso I didn't but since females don't have the big claw I was wondering if they would catch and kill my fish? Basically, my questions are if I got a fiddler female crab would she kill any of my fish even if I kept her well fed and if I could get 2 female crabs, would they like crawl together ? Or..