Cook the elbow macaroni in a large pot of boiling salted water according to the package instructions until al dente. Drain and rinse under cold water to cool; set aside.
While the pasta is cooking, hard boil the eggs, then peel and dice them.
In a large mixing bowl, combine the cooled macaroni, flaked crab meat, chopped shrimp, chopped celery, green onions, and diced hard boiled eggs.
In a small bowl, whisk together the mayonnaise, Greek yogurt, dill pickle relish, and sugar until smooth. Season with salt and black pepper to taste.
Pour the dressing over the pasta mixture and gently stir until all ingredients are well coated.
Cover the salad and refrigerate for at least 2 hours, or overnight, to allow the flavors to meld together.