I am a self proclaimed crawfish cooking expert! I personally would ditch the other shell fish and just cook the crawfish. Or atleast cook them seperate. They will turn out better that way. Here's how I cook my mud bugs.
1. Thoroughly rinse crawfish with a garden hose.
2. Use 50 oz. of "Louisiana" brand powdered crab boil if you can find it. If not, get Zatarans. This is enough to cook 40 lbs of craw fish.
3. Bring crab boil to a boil along with a stick of butter. (Makes them easier to peel.)
4. Add small red potatoes and crawfish. Bring back to a rolling boil and cook covered for 5 minutes. Turn off heat.
5. Add corn, mushrooms, sausage. Let soak uncovered for 15-25 minutes depending on how spicy you want them.
6. Pour crawfish out and squeeze fresh lemon over the top of them.
7. Dig in and don't forget to suck a few heads!
Let us know how they turn out!