I am not an expert, but when I lived in Louisiana I attended many boils, and have my own boiling set up. So, you purge them with salt water first. Then you get some Zatarains Crab Boil mix. Use both the powder and the liquid both. Or some use Old Bay, (not as good)
Then get a big pot and heat it up to boiling with a lot of salt. You add your crab boil mix and then add anything that sounds good to you along with the Craw fish.
Onions, potatoes, sausage, mushroom's, carrots, other fish (in a onion sack so as not to fall apart. ect.
It is one of the best meals I have ever had, and I have been around.
There is a science to making sure they are done. You don't want overdone, but if underdone just put back in.
If you have any questions just ask.