Question for you master boilers - boil crawfish or crabs first?

My brother tells me that crabs really dirty the water and it isn't good to cook crawfish after crabs in a boil. He also suggested not to boil all your fixins with the crabs either. Supposedly they puke like crazy once they get in the pot and it messes up the fixins (corn, potatoes)

I've got 2 sacks of crawfish and a bushel of crabs. The easiest way would be to boil the sacks then the crabs. However if I did the crabs in the middle I'd have to change the water for the last sack of crawfish.

What say you masters of the boil? I think my brother is full of it, but he has been right a few times on things.

I'm rolling with Captain Sid's seasoning, oranges, lemons, onions, garlic, green beans, corn, potatoes, more garlic, onions, shrooms, conecuh sausage. First boil of the season for me, so I want it to be perfect!!!