Best fish soup or stew (no shellfish)?

OOPs, didn't specify. You would be making two pans of cioppino, one with shellfish, one without.

I love cioppino.
How many people have the allergy? Since it makes a huge amount after the cod (white fish fillets) and shrimp, you can remove several cups of broth and non-allergic items, then add clams or mussels. When serving, no one needs to know that "A" has a different version of the dish.

Maybe consider a seafood paella.
You can also add in some chicken and/or chorizo. Remember, rice is nice!

I've made Drbabs' gumbo and would highly recommend it. And although I haven't yet made it, I have my eye on inpatskitchen's salmon chowder, http://www.food52.com/recipes/16003_very_simple_salmon_chowder - you can use fish stock or, if you can eat shrimp, shrimp stock.

Can you eat shrimp? http://food52.com/recipes/3528_shrimp_gumbo
This is also really good--you could eliminate whatever your family members are allergic to, and increase the fish, maybe use 2 different varieties:
http://food52.com/recipes/14754_dads_favorite_seafood_stew
And I haven't made this, but Rivka's recipes are all really good, so i'm sure this one will be:
http://food52.com/recipes/992_huachinango_a_la_veracruzana_red_snapper_veracruz_style

I think that a white fish (hake, cusk, pacific halibut or a line-caught cod) and chorizo is always a great combination. You could use this recipe as a base: http://www.food52.com/recipes/2906_oyster_stew_with_chorizo_and_spinach

But just swap in the white fish for the oysters and a fish stock for the oyster juice.

Sorry that is " salmon moqueca" (:'#* iPad) recipe of winnieab