What kind of crays are they? Unless they are CPO's or cajuns (C. Patzcuarensis or C. Shufeldtii) they will probably make snacks out of the bloodfins. If they are not dwarfs, their 10G is already overstocked.
I know you are trying to find a good home for the bloodfins since your tank is too small for them, but bloodfins should have something more like a 20g and need to be in a school.