What to do with unwanted marbled crayfish?
They're generally small, so they wouldn't make much of a meal.
You could move them into an indoor aquarium. Lots of people report that compared to many other crayfish species, marbled crayfish aren't as likely to eat other tank mates. They are omnivorous, and will take out fish if they get the opportunity, so the risk is lower, but not zero. And being omnivorous means they'll also make a meal of any aquarium plants.
Lots of people feed marbled crayfish to fish in their aquariums. Oscars are common aquarium fish that are predators, and they love crayfish. If you go to YouTube, you can find lots of videos of oscars eating crayfish.
If you wish to dispose of them, I suggest freezing. Cold acts as an anesthetic.
If you have lots, I might be able to find some researchers who would be willing to take them off your hands.
