Hi,
Don't mean to be disagreeable, but I have housed Clarkii, Alleni and marbles crayfish with various live bearers without incident. One mistake people make is they don't feed the crayfish and keep the tank free of good food sources. If you were a crayfish, what would you do??
If you provide enough hides, I have strip tanks and use 4" sections of PVC 2x per crayfish you should be fine. I feed mine blanched froozen peas cut in half. They love them and gorge on them. If you want to keep them busy longer, let the half pea sit out an hour or two. As it gets dryer it becomes more difficult for them to eat quickly. I will also use a very small piece of a sinking shrimp pellot 1-2 x weekly. They get in a feeding routine quickly and if you feed them 5 min. prior to lights out you will not have a problem.
Keep in mind no live plants or bottom dwellers like corys. Long finned fish like bettas are pushing your luck as well. Good luck and enjoy them as they are very cool.
P.S. Marble crayfish are a great supply of live food as they clone.