Welcome to the board Richard!
The only crawfish I've eaten have been deep fried at a restaurant. I'm bettin' that you're right. Everything tastes better grilled than boiled. Boiling takes flavor out, while grilling adds flavor! If you're doing a gumbo then the flavors blend in a broth and you still get it. But I'll guess you inlaws are draining it away.
I agree with Grand Scale and our guest that if you'll treat them like jumbo shrimp, and grill them on skewers, you'll have some good eatin'!