Soak 8 8-inch wooden skewers in warm water for at least 45 minutes before using. Thread pork, chicken, and shrimp on skewers, keeping them separate, and place skewers in a shallow glass baking dish. In workbowl of a food processor combine parsley, oil, onion, basil, garlic, lemon juice and zest, salt and cayenne. Process until smooth. Pour marinade over skewers and turn them several times to coat well. Marinate 30 minutes at room temperature or cover and refrigerate up to 3 hours, turning skewers several times. Preheat grill. Add skewers, pork first, then chicken, then shrimp, and grill until browned on all sides.