Prepare a charcoal fire using about 6 pounds of charcoal and burn until the coals are completely covered with a thin coating of light gray ash, 20 to 30 minutes. Spread the coals evenly over the grill bottom, position the grill rack above the coals, and heat until medium-hot (when you can hold your hand 5 inches above the grill surface for no longer than 3 or 4 seconds). Or, for a gas grill, turn on all burners to high, close the lid, and heat until very hot, 10 to 15 minutes.
In a large bowl, combine the chicken, shrimp, sausage, tomatoes, okra, onion and shisito peppers. Add the oil and Creole seasoning, and toss to evenly coat the ingredients. Thread the shrimp, tomatoes and okra onto separate skewers. (The chicken, onions, and shisito peppers will go directly on the grill. If using pepper strips, thread onto skewers.) You could skewer and then season, but coating ahead of time ensures an even coating of spices — and messy fingers, but you can always wash your hands!
Now, it’s a matter of cooking in batches, working the grill, and trying to make sure everything is ready about the same time. However, don’t overthink this — set a second bowl beside the grill and as the items are ready, simply toss them into the bowl and cover to keep warm.
Place the chicken pieces on the grill and cook until firm, turning once until the juices run clear when pierced with a knife and the center registers 165 degrees, about 4 minutes per side. Meanwhile, place the onions and peppers on the grill and cook until tender and charred, about 7 minutes. Add the okra and tomatoes to the grill and cook until charred and tender, about 5 minutes. Arrange the sausage over slightly cooler heat and cook until charred and warmed through. Towards the end of cooking when everything is nearly done, add the shrimp and cook, turning once or twice, until the shrimp is opaque, about 2 minutes per side.
Transfer the cooked ingredients to the second large bowl, removing from the skewers as needed. Top with the warm ketchup and scallions and toss to coat. Cover the mixture tightly with plastic wrap and let the vegetables steam and wilt slightly, about 3 minutes. Remove the plastic wrap. Taste and adjust the seasoning with salt, pepper and Creole seasoning to your liking. Serve immediately with additional hot sauce on the side.