Soak rice in 4 cups warm water with lemon overnight for at least 12 and up to 24 hours. Drain.
1. In a large saucepan, heat the olive oil. Add the onion, season with salt and pepper and cook over medium heat, stirring, until soft and translucent. Add the rice and cook for 1 minute, stirring to thoroughly coat. Crumble the saffron into the wine and add it to the rice. Cook, stirring until the wine is absorbed. Add 1 bottle clam juice and cook, stirring constantly, until nearly absorbed. Continue adding the clam juice 1 bottle at a time, stirring constantly until it is nearly absorbed between additions. The risotto is done when the rice is al dente and suspended in a thick, creamy sauce, about 25 minutes total. Season with salt and pepper.
2. Melt the butter in a large skillet. Add the shallot and cook over medium heat until softened, about 2 minutes. Add the shrimp and crab and cook until just heated through. Scrape the seafood into the risotto and stir in the parsley. Serve immediately.